This book reviews Cantonese syllable and Japanese mora structure, and the findings of recent studies of their durational characters. Cantonese speakers’ both durational perception and actual mishandling of Japanese words data were analyzed, and durational L1 transfer was demonstrated. Examples of mishandlings are all collected from the author’s students of Japanese, and Cantonese perceptional questionnaire was conducted in her Japanese language classes. The elements of Cantonese length have an effect on mastering Japanese for Cantonese speakers. It will be a guide for Cantonese learners seeking to know their durational shortcomings of pronunciation and how to improve them. It will be also useful for Japanese language instructors wishing to understand Cantonese learners’ phonological features.