This study examined the perception of short and long vowels in Arabic and Japanese by native Japanese (NJ) and nonnative learners of Japanese (NNJ). Ten Japanese vowels (5 short, 5 long) were given as response categories. As expected, the NJ listeners categorized the Japanese vowels more accurately than did the NNJ listeners (91 vs. 83%). Further, the NJ listeners tended to identify Japanese long vowels correctly more often than short vowels (93 vs. 88%), but the NNJ listeners did not show this pattern (82 vs. 84%). Both NJ and NNJ listeners assimilated short Arabic vowels to a wide range of Japanese vowels.