This study investigated L2 production, perception, and the relation of production and perception by examining 20 Korean learners’ production and perception of the English contrasts of /ʃ/ vs. /ʃi/, /ʧ/ vs. /ʧi/, and /ʤ/ vs. /ʤi/ in word final position. Of the 20 Korean learners, 10 (5 males, 5 females) were low in English proficiency and the other 10 (5 males, 5 females) were high. Our findings from production and perception experiments showed that the relation of L2 production and perception varies according to learners’ proficiency levels in L2. A significant correlation between L2 production and perception was attested within the high group learners. Thus, the high group learners with higher production accuracy generally exhibited higher perception accuracy. Unlike the high group, the low group learners’ production and perception patterns did not show any significant correlation between the two. In general, the low group displayed higher accuracy in production than in perception. In addition, within the low group, the heavy influence of L1 constraints on L2 perception was attested while L2 production was not in accordance with L1 phonology.