We used housing data from a Chinese college to examine peer effects on students' major persistence and major choices after dropping out of their initial majors. Random checks were performed to ensure that student peers--dormitory roommates and social group mates--were randomly assigned according to a few known factors. In addition, two peer groups with different peer-to-peer relations allowed us to observe whether close peer relations were more influential than acquaintances in major transfer decisions. Results indicated strong peer effects on students' major transfer. Having more peers in the same major moderately increased students' persistence rate in their initial majors. In addition, when one's peers in the same major dropped out of their initial major, he or she became more prone to dropping out as well. Students' choices of destination major after leaving their initial majors were also affected by the major choice of their transferred peers. Finally, peer effects were stronger when students had closer peer relations.