This study examined the extent to which variation in speaking rates and phonemic vowel length affect formant movements in Japanese vowels. Two male native speakers of Japanese produced the ten Japanese vowels (5 short and 5 long) in the /mV(V)mV/ context in a carrier sentence at three speaking rates (slow, normal, fast). The first two formant frequencies at the midpoint and the formant trajectory in the entire vowel duration were analyzed. The long vowels occupied a more peripheral portion of the F1-F2 vowel space than the short vowels did. This supports a suggestion that long vowels resist coarticulation to a greater extent than short vowels do. Effect of vowel length interacted with effect of speaking rates for /e/, /o/, and /a/. For example, the short mid vowels /e o/ were more susceptible to change in speaking rates than the long counterparts. In contrast, the high vowels, /i/ in particular, showed limited effects of rates and vowel length, thus reinforcing the notion of point vowels.