MU Online Resolution Settings – Full Guide

This guide explains how to change your MU Online resolution and window mode in two ways:

  • Using the launcher.exe (modern servers – easiest way).
  • Manually editing LauncherOption.if (advanced / older clients).

Use the launcher method if your server supports it. Only use manual editing if you need a specific resolution, are fixing a bug, or your launcher does not show the resolution options correctly.

1. Changing Resolution via launcher.exe (Modern Servers)

On most modern Season 20+ servers, you can set your resolution directly in the game launcher before you click Start Game.

Recommended Always try the launcher first. It is safer than editing files, works on most modern servers, and usually includes a drop‑down list of supported resolutions and a Window Mode checkbox.

Steps (Launcher Method)

  1. Open your MU Online client folder and run launcher.exe (or the shortcut your server provides).
  2. Look for a button such as Options, Settings or a gear icon.
  3. In the settings window:
    • Select your desired Resolution from the drop‑down list (for example, 1280×720, 1920×1080, etc.).
    • Choose Window Mode or Full Screen (names vary per server).
  4. Click OK or Apply to save your settings.
  5. Click Start Game on the launcher to enter the game with the new resolution.
Tips for modern setups:
• For 1080p monitors, use 1920×1080 if available, or 1280×720 for better performance.
• For multi‑monitor or heavy alt‑tabbing, enable Window Mode (or borderless/windowed full screen if your launcher supports it).

2. Changing Resolution via LauncherOption.if (Manual Method)

Some older clients or custom servers still use a configuration file like LauncherOption.if (sometimes named LauncherOption.ini or similar). You can edit this file directly to change resolution and window mode.

Advanced Warning: Only use this if you know what you are doing. Always close the game and launcher and make a backup of the file before editing.

2.1. Finding and opening LauncherOption.if

  1. Close MU Online completely (both game and launcher).
  2. Open your MU Online game client folder (where main.exe or launcher.exe is located).
  3. Find the file named LauncherOption.if (or similar).
  4. Right‑click the file > Open with > Notepad (or Notepad++).

Inside the file you will see something like: 

// DevModeIndex controls the resolution
// 0: 800x600 (4:3)
// 1: 1024x768 (4:3)
// 2: 1152x900 (4:3)
// 3: 1280x720 (16:9)
// 4: 1280x800 (16:9)
// 5: 1280x920
// 6: 1440x900 (16:10)

DevModeIndex:3

// WindowMode: 1 = Windowed, 0 = Full Screen
WindowMode:1

2.2. DevModeIndex – Resolution List

The DevModeIndex setting selects which resolution the game will use. Each number represents a specific resolution:

DevModeIndex Resolution Aspect Ratio Notes
0 800 × 600 4:3 Very low; compatible with very old PCs/monitors.
1 1024 × 768 4:3 Classic default MU resolution.
2 1152 × 900 4:3 Slightly bigger 4:3 resolution.
3 1280 × 720 16:9 HD, very good for most modern 16:9 monitors.
4 1280 × 800 16:9 Good for some laptop screens; slightly taller than 720p.
5 1280 × 920 – Custom resolution; availability may depend on client.
6 1440 × 900 16:10 Good for 16:10 monitors and some older widescreens.
Note: Some clients may include extra DevModeIndex values (for example, 7, 8, 9…) for higher resolutions like 1680×1050 or 1920×1080. Always check the comments inside your LauncherOption.if file or your server’s website for additional entries.

2.3. WindowMode – Full Screen vs Windowed

The WindowMode setting controls whether MU runs in full screen or in a window:

WindowMode Mode Description
0 Full Screen Game covers the whole screen. Better immersion, but alt‑tabbing can be slower.
1 Windowed Game runs in a window. Easier to alt‑tab and multi‑task.

Some servers emulate “borderless full screen” by using windowed mode plus custom launcher settings, but with only WindowMode:0/1 available you usually have just these two options.

2.4. Step-by-step: editing the file

  1. Close MU Online and the launcher.
  2. Open LauncherOption.if with Notepad.
  3. Find the line that starts with DevModeIndex and change the number:
    • For example, set it to 3 for 1280×720: 
      DevModeIndex:3
  4. Find the line that starts with WindowMode and set it to:
    • WindowMode:0 for full screen
    • WindowMode:1 for windowed mode
  5. Save the file (Ctrl + S) and close Notepad.
  6. Run launcher.exe and start the game. It should now use the resolution and mode you selected.
Backup tip: Before editing, copy LauncherOption.if to something like LauncherOption_backup.if. If something goes wrong, delete the broken file and rename the backup back to LauncherOption.if.

3. Which Resolution Should I Use?

You don’t always need the highest resolution. MU Online scales in a way where text and UI can become very small at very high resolutions. Here are some simple recommendations:

  • Low-end PC: 1024×768 or 1280×720 for better FPS.
  • Standard 1080p monitor: 1280×720 (easier to read UI) or, if your client supports it, 1920×1080.
  • 16:10 monitor: 1440×900 is usually a good fit.
  • Streaming / recording: 1280×720 (720p) is the sweet spot for many streamers.

4. Common Problems & Fixes

Game opens off-screen or on the wrong monitor

  • Set WindowMode:1 (windowed), start the game, drag it to the correct monitor, then exit and restart.
  • Try a smaller resolution like 1280×720 to make sure the window fits on your screen.

Game is too small or too big

  • If everything looks tiny, use 1280×720 or 1280×800 instead of higher values.
  • If the game doesn’t fit properly, pick resolutions that match your monitor aspect ratio (16:9 or 16:10).

Text looks blurry in windowed mode

  • Right‑click main.exe or launcher.exe > Properties > Compatibility.
  • Check Change high DPI settings and experiment with overriding the high DPI scaling (Windows 10/11 feature).

Launcher keeps overwriting my settings

  • Some launchers rewrite LauncherOption.if based on their own UI settings.
  • In that case, always change resolution from launcher.exe instead of the file.

Conclusion

For most players on modern servers, the easiest way to change resolution is through launcher.exe. If your server uses the LauncherOption.if file, you can still fully control resolution and window mode by editing DevModeIndex and WindowMode.

Pick a resolution that matches your monitor and feels comfortable for your eyes, enable window mode if you alt‑tab a lot, and you’ll have a much better MU Online experience.