This book constitutes the refereed proceedings of the 21st China Conference on Machine Translation, CCMT 2025, which took place in Lanzhou, China, during September 26–28, 2025.

The 6 full papers included in this book were carefully reviewed and selected from 6 submissions. The conference has been a highly productive forum for progress in this area and is considered a leading and important academic event in the natural language processing field in China.