What is the MTZ file format?
An .mtz file is a theme package used by Xiaomi's MIUI and HyperOS operating systems on Android devices, including Xiaomi, Redmi, and POCO phones and tablets. Internally it is a standard ZIP archive, identifiable by the PK magic bytes (50 4B 03 04) at offset 0 - renaming an .mtz to .zip lets any archive utility open and inspect its contents.
The archive bundles all visual and audio assets that define a custom UI skin:
icons/- replacement launcher and system app iconswallpaper/andlockscreen/- home and lock-screen wallpapersfonts/- optional custom typefacesringtones/orsounds/- notification and system soundsframework/- preview thumbnails and additional UI resourcesdescription.xml- metadata declaring the theme name, author, and target MIUI/HyperOS version
Entries are compressed with DEFLATE; per-entry CRC-32 provides basic integrity checking. There is no theme-level digital signature.
Themes are installed through the built-in Xiaomi Themes app; the .mtz package cannot be side-loaded as an APK - it is applied by the theming engine inside MIUI or HyperOS, not installed as a standalone application.
Note that .mtz is an overloaded extension: unrelated formats - including the CCP4 crystallography MTZ format used in X-ray diffraction software - share the same suffix but have an entirely different binary structure.
Security & safety
RISK: MEDIUMA theme is mostly resource data, but MIUI themes can change deep UI components (lock screen, fonts, system styling), and historically some third-party .mtz themes have hidden ads or pushed unwanted changes. Install themes from Xiaomi's official Themes store where possible; be cautious with .mtz files from random forums or sites that ask you to disable security checks. On a PC the file is inert (just a ZIP) and safe to inspect.
Format details
in a nutshell- CCP4 MTZ (crystallography) - In macromolecular crystallography, .mtz is a binary reflection-data file from the CCP4 suite - unrelated to phone themes.
- Viewpoint MetaStream/MTZ scene - Legacy Viewpoint Media Player used a compressed .mtz 3D scene format; the player and format are long defunct.
Programs that open MTZ files
Windows1 app
7-Zip
Open-source Rename the .mtz to .zip (or open directly), then extract to inspect icons/wallpapers/fonts. Cannot apply the theme - view only. 
macOS1 app
The Unarchiver
Free Open the .mtz as a ZIP to browse its contents. For inspection only; themes apply only on the phone. 
Android2 apps
Xiaomi Themes (built-in)
Built-in Copy the .mtz to internal storage (e.g. Downloads or /MIUI/theme), open the Themes app, and import/apply it; or install themes directly inside the Themes store.
MTZ Manager (third-party)
Free On some non-Xiaomi phones, use a community MTZ manager app to apply parts of a theme. Support is partial - built-in Themes is preferred on Xiaomi. Technical details
deep spec| Container format | Standard ZIP archive; any ZIP-capable tool can open an .mtz file |
| Magic bytes | 50 4B 03 04 ("PK") at offset 0 - identical to a standard ZIP local file header |
| MIME type | application/zip (commonly served as application/octet-stream for downloads) |
| Encoding | Binary |
| Byte order | Little-endian (ZIP specification) |
| Compression | DEFLATE per entry (standard ZIP); uncompressed entries also permitted |
| Integrity checking | CRC-32 checksum per ZIP entry; no theme-level digital signature |
| Required manifest | description.xml inside the archive root - declares theme name, author, and target MIUI/HyperOS version |
| Asset directory structure | icons/, wallpaper/, lockscreen/, fonts/, ringtones/ (or sounds/), framework/ for preview resources |
| Target platform | Android running MIUI or HyperOS (Xiaomi, Redmi, POCO devices) |
| Installation method | Applied by the built-in Xiaomi Themes app theming engine; cannot be sideloaded like an APK |
| Typical file size | A few MB to tens of MB, depending on bundled wallpapers, fonts, and audio assets |
| Maximum archive entries | Up to 65,535 files (standard ZIP directory limit) |
| Version targeting | Manifest declares the supported MIUI/HyperOS version; themes may be incompatible across major OS generations |
| Extension collision | The .mtz suffix is also used by the unrelated CCP4 crystallography reflection-data format - distinguished by magic bytes and context |
| Released | 2010 (MIUI on Android); still used on HyperOS |
| Latest version | Current MIUI/HyperOS theme package |
MTZ conversions
Community Q&A
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