Objective: To examine the habit of napping and its relationship with nighttime sleep in college students. Participants: Four hundred and forty undergraduate students who responded to an anonymous online survey in April 2010. Methods: Three questions were asked to determine the frequency, length, and timing of napping during the past month. Sleep quality was measured by the Pittsburgh Sleep Quality Index (PSQI). Results: The PSQI score significantly differed among self-reported nap-frequency (p = 0.047) and nap-length (p = 0.017) groups, with those who napped more than 3 times per week and those who napped more than 2 hours having the poorest sleep quality. Students who napped between 6 and 9 pm had shorter sleep on school nights compared with students in other nap-timing groups (p = 0.002). Conclusions: College students who are self-reported frequent, long, and late nappers may have a higher risk of poor nighttime sleep quality and more severe sleep deprivation.