Compared to stress-timed English, mora-timed Japanese is characterized by a simpler syllabic structure and no vowel reduction. Such differences may explain some aspects of the problems that Japanese talkers have in producing English speech rhythm, i.e., an L1 influence on L2 rhythm production. The present study tested whether this L1 influence on L2 could be moderated by an increase in L2 experience. We examined English sentences spoken by Japanese (‘experienced’ and ‘inexperienced’ English learners) and native Australian English talkers. The mean duration and variability of consonant and vowel intervals were calculated using rhythm metrics. The results showed that the mean duration of phoneme intervals was relatively longer in L2 speech, particularly the inexperienced L2, compared to L1 speech. Furthermore, the inexperienced L2 talkers exhibited the least vowel durational variability, with the English talkers having the most; the values of the experienced L2 talkers were intermediate. Differences among the talker groups were well described by the coefficient of variations of vowel and consonant durations, more specifically, durational variability increased as the phoneme duration got shorter. Overall, the results demonstrated that an L1 influence on L2 speech rhythm production decreases as a function of L2 experience.