Acoustic manipulation of Japanese prosody by English speakers was investigated. The study examined how fluent Japanese speakers of English realize Japanese lexical accent in terms of mora duration and the fundamental frequency, and also whether they transfer acoustic features associated with English word stress to Japanese lexical accent. The experimental results found that more fluent speakers of Japanese used F0 to indicate lexical accent without increasing mora duration, whereas less fluent speakers did not, and instead increased the duration of accented vowels at the same time suppressing the F0 increase. The results also found that the English speakers were unable to produce non-accented words and place an accent in a word, which triggers downstep. Moreover, they tended to place an accent in each word rather than using a phrase accent, which caused an overall impression of foreign accent despite a good control of speech rhythm.