MOBI is an ebook format from Mobipocket SA that Amazon adopted for Kindle. Inside sits a binary wrapper around HTML text, images and an OPF manifest. Amazon KDP has refused fixed layout MOBI uploads since March 2025. EPUB is the open format Amazon recommends for new reflowable titles.
You open a .mobi file and wonder how it differs from EPUB or other Kindle files. MOBI has a short history and Amazon now favors other formats.
Facts follow the Library of Congress page on Mobipocket and the Amazon KDP file formats page.
What is a MOBI File?
Mobipocket SA introduced the format in 2000 for reflowable ebooks. Amazon acquired the company in 2005 and used the format for Kindle devices launched in 2007. Mobipocket.com stopped distributing ebooks in late 2011.
Files began with the .prc extension and later used .mobi. Its Internet media type is application/x-mobipocket-ebook.
What is Inside a MOBI File?
| Part | Detail |
|---|---|
| Base | Palm OS PRC format related to PalmOS DOC |
| Content | Binary wrapper around HTML text, images and an OPF manifest |
| Header | 16 byte header then Record 0 with a MOBI header, optional EXTH header and the title |
| Marker | Text BOOKMOBI at byte 61 |
| KF8 | Newer content with HTML5, CSS3, embedded fonts and fixed layout |
Late 2011 combination files pair Mobi 6 content with KF8 content.
Does Amazon Still Use MOBI?
Amazon states that since March 2025 KDP rejects MOBI files for fixed layout titles. KDP now takes EPUB, KPF, DOC, DOCX, HTML, RTF and TXT. Amazon recommends EPUB for new reflowable titles.
Amazon never published full documentation of the format. Most knowledge comes from reverse engineering by tools like KindleUnpack and Calibre.
How do You Open a MOBI File?
- Kindle devices. Every Kindle generation opens non DRM .mobi files as of early 2019.
- Ebook software. Calibre opens and converts MOBI files.
- Other readers. Convert the file to EPUB when your reader lacks MOBI support.
DRM protected Mobipocket ebooks open only in the apps tied to your purchase.
Related reading: the ICS file format and how to rename many file extensions at once.
Frequently Asked Questions
What is a MOBI File?
It is an ebook format from Mobipocket that Amazon adopted for Kindle.
Is MOBI the Same as EPUB?
No. EPUB is an open standard. MOBI is proprietary and only partly documented.
Does Kindle Open MOBI Files?
Yes. All Kindle generations open non DRM .mobi files as of early 2019.
Does Amazon KDP Accept MOBI?
Not for fixed layout titles since March 2025. Amazon recommends EPUB for new reflowable titles.
What is KF8?
It is the newer Kindle content layer with HTML5, CSS3, embedded fonts and fixed layout.
Key Takeaways
- Mobipocket SA introduced MOBI in 2000.
- MOBI wraps HTML text, images and an OPF manifest.
- KDP refused fixed layout MOBI uploads from March 2025.
- EPUB is the open format Amazon recommends.
- Calibre opens and converts MOBI files.
Sources and References
Facts follow the Library of Congress and Amazon pages.
- Mobipocket ebook format (Library of Congress) www.loc.gov
- File formats (Amazon KDP Help) kdp.amazon.com