Sleep is a naturally recurring state of mind and body which is a vital human physiological process. The sleep quality of nurses has become a prominent social focus since they are engaging in work based on a shift schedule. The paucity of data available on sleep quality and associated factors in Sri Lanka led this study to be conducted among nurses at Apeksha Hospital, Sri Lanka. A descriptive cross-sectional study was conducted among 215 nurses at Apeksha Hospital, using a simple random - sampling method. A self-administered structured questionnaire was used as the data collection instrument and Pittsburgh Sleep Quality Index (PSQI) was used to measure the sleep quality among nurses. The majority (86.5%) were females. Of the participants 65.58% had deficient sleep (PSQI≥5) and 34.42% had healthy sleep (PSQI<5). The mean score of the sleep quality was 7.16±3.30. Sleep quality was significantly (p<0.05) associated with chronic symptoms (p=0.003), children status (p=0.007), night shift frequency per month (p=0.029), number of patients per night shift (p=0.048), number of working hours per week (p=0.001), sleep duration (p=0.032), sleep disturbances at night (p=0.001), sleep medication use (p=0.020), and daytime dysfunction (p=0.001). In conclusion, sleep quality was poor among nurses working at Apeksha Hospital, Sri Lanka. The characteristics of night shifts, such as number of shift duties, number of hours, and number of patients in the night shift, were associated with the sleep quality of nurses. Therefore, scheduling working hours and night shifts according to the `national and international guidelines are vital.