This study examined whether vowel onset intervals in Japanese disyllables can serve as a reliable timing unit in Japanese. Duration of vowel onset intervals was measured in Japanese disyllables containing singleton and geminate stops spoken in a carrier sentence at three speaking rates. Analysis included the vowel onset interval duration divided by the mean mora duration, and this value was predicted to show timing regularity in terms of the mora, in accordance with Brady Port and Nagao, 2006. Results supported this prediction.