Purpose The purpose of this study was to explore postpartum women's sleep quality and its predictors in Taiwan. Design Cross-sectional design. Methods Postpartum women (N= 327) were recruited during their postnatal check-ups in Taiwan. Data were collected from October 2008 to July 2009 using a demographic form, the Pittsburgh Sleep Quality Index (PSQI), Physical Symptoms Checklist, Perceived Stress Scale, and Postpartum Social Support Scale. Descriptive statistics, Pearson's correlation, and stepwise multiple regression analysis were used to analyze data. Results Most participants (87.5%) reported poor sleep quality (PSQI> 5). Postpartum sleep quality was predicted by postpartum physical symptoms, frequency of nighttime awakening, co-sleeper disturbance, marital satisfaction, perceived stress, and baby sleep status, which explained 29.9% of the total variance. Conclusions Most postpartum women did not sleep well due to physical discomfort, perceived stress, co-sleeper disturbance, and marital dissatisfaction. Clinical Relevance Evaluation of sleep quality should be a routine part of postnatal check-ups. Information on women's sleep problems, marital satisfaction, stress, co-sleepers, and baby sleep status can be used to individualize intervention protocols for sleep-disturbed women.