Objectives: The general purpose of this study was to investigate the effect of night shift work (NSW) on insomnia, anxiety, depression, and fatigue, among nurses working in critical care units. Methodology: Five hundred and twelve critical care nurses were recruited from the Intensive Care Units (ICU), Emergency Rooms (ER) and Operation Rooms (OR) from six major hospitals in Amman, Jordan. Participants singed an informed consent and answered, sociodemographic questionnaire, in addition to Hospital Anxiety and Depression Scale, Fatigue Severity Scale, and Insomnia Severity Index. Results: Critical care nurses who were working on night shift have higher levels of insomnia, depression, anxiety, and fatigue than nurses working on day shift or temporary night. Furthermore, female and ICU nurses experienced more fatigue than male nurses and nurses from OR and ER respectively. There was a dose-response relationship between the number of night that nurses work in the previous year with their (insomnia, depression, and fatigue levels) Conclusion: Night shift work induced insomnia for nurses working in critical care units which increased their anxiety, depression and fatigue levels. This has negative consequences in their health 138 Mohannad Eid AbuRuz and Haneen M. Abu Hayeah and the care provided to the patients. Health care employers should use alternative methods to help nurses overcome this issue.