Background and Aim: Adequate sleep is considered as one of the physiological needs of human beings. In addition to adverse effects on physical and mental health, inadequate sleep can affect cognitive functions as well. Since night shifts are part of the main tasks of most clinical residents and are followed by changes in their sleep rhythm, this study investigated the changes in cognitive functioning of clinical residents following night shift work. Materials and Methods: This descriptive-correlational study was conducted by convenient sampling method. So, 104 clinical residents were selected from seven different clinical specialties at Shahid Beheshti University of Medical Sciences hospitals. In order to investigate the cognitive function of the residents, the Demographic Questionnaire and Cognitive AbilitiesQuestionnaire were used in the beginning and end of the shifts. Data were analyzed using SPSS software and statistical tests such as the Paired T-test, Wilcoxon, independent T-test, the Spearman and Mann-Whitney. Results: According to statistical analysis, the mean score of memory scale at the end of the shift work was significantly different between different specialties (P<0. 05). The difference in memory score changes at the end of the shift, compared to the beginning of the shift, in non-surgical specialties was significant (P<0. 05). It was also found that a significant relationship existed between the overnight sleep in the shift and the memory scale at the end of the shift (P<0. 05). Conclusion: In this study, findings showed that night shift in various parameters, such as inadequate and inappropriate sleep, has caused changes in some cognitive function scales in different academic years and different clinical specialties. Differences in workload, job stress level, coping mechanisms and responsibility level could be the main reasons for these differences in different academic years and clinical specialties.