This study investigates the effects of immediate repetition of auditory words on L2 pronunciation improvement of English schwa by Japanese EFL learners. More specifically, the study is concerned with how the amount of input (i.e., five or ten repetitions) and stimuli characteristics (i.e., the position of schwa in a word, word familiarity) influences the repetition effect. The study consists of a study and a test phase: In the study phase, participants listened to and repeated words. In the test phase, they repeated spoken stimuli including previously heard as well as new words, both ten minutes and one week after the study phase. The auditory materials consisted of 32 real words. The duration ratio of schwa to a stressed vowel in a word and the quality of the schwa were acoustically examined. A repetition effect was mainly found in the durational aspect. Repeating the stimuli more than five times did not differentiate the effect. One week after the study phase, the effect persisted only for initial schwa, which is weakly represented in the participants' mental representation. The pedagogical implications for L2 pronunciation teaching from the view of language processing are discussed.