This study explores the relationship between the introversion‐extraversion tendencies of Japanese students and their proficiency in English as a foreign language (EFL). It was hypothesized that in an EFL situation, extraverted students would attain a higher proficiency in English because they may take advantage of the few available opportunities to receive input in English and practice the language with native speakers. In order to test the hypothesis that extraverts are more proficient in English, 80 junior college English students and 105 adult school English students took a standardized English test, completed a personality questionnaire, and provided information on a biodata form. In addition, 45 of the junior college students participated in English oral interviews which were then rated for proficiency by two evaluators.The hypothesis that extraverts are more proficient in English was not supported. In fact, statistical analysis revealed that extraversion had a significant negative correlation with pronunciation, a subcomponent of the oral interview test. In addition, introverts tended to have higher scores on the reading and grammar components of the standardized English test.Even though introverts tended to score better on most of the English proficiency measures, it was found that junior college males who had tendencies towards extraversion had higher oral interview scores. Extraversion also correlated positively with length of time spent studying English at the adult school. These findings are discussed with respect to cultural factors predominant in Japanese society and psychological theor