Literature from education, educational psychology and second language acquisition has consistently found that self-efficacy is a key factor leading to increased language learning success. Students with more self-efficacy are claimed to have higher motivation and to expend more effort in the learning process. On the other hand, those with less self-efficacy give up more readily when they encounter difficulty. Teacher feedback on L2 writing has been claimed to decrease student L2 writing self-efficacy, whereas some have suggested that peer feedback has a more positive impact on learners' self-efficacy. The present study compares changes in self-efficacy over a period of one academic year between two groups of Japanese university students. One group received teacher feedback on every preliminary draft for the one-year period while the other group gave and received peer feedback on every preliminary draft over the same period. It was found that the teacher feedback group increased in writing self-efficacy significantly more than the peer feedback group.