Objective: The aim of this study was to investigate the relationship between stress and cognitive flexibility levels of nursing students. Method: The population of the research, which was carried out in a descriptive and cross-sectional type, consisted of 1213 students who received education in a nursing faculty in Istanbul in the 2017-2018 academic year. Its sampling was composed of 292 nursing students who were stratified, and calculated by a formula with a known number of elements, accordingly a total of 292 nursing students were included in the study. As data collection tools, Personal Information Form, Perceived Stress Scale (PSS) and Cognitive Flexibility Scale (CFS) were used. The data obtained; were analyzed using appropriate statistical methods. Results: The mean age of the nursing students was 20.30±1.54 years, 82.5% of them was female, 99.3% of them was single and 89.4% of them was unemployed. The students’ mean Perceived Stress Scale score was 27.53±7.00 and the mean Cognitive Flexibility Scale score was 39.43±2.83. There was a statistically significant negative correlation was detected between Perceived Stress Scale and Cognitive Flexibility Scale scores (p<0.05). Perceived Stress Scale scores of women were found to be significantly higher than males (p<0.05). Conclusion: According to these results, it has been observed that the students’ stress and cognitive flexibility levels are at moderate levels. There are factors affecting the levels of stress and cognitive flexibility in nursing students.As students’ perceived stress levels increases, their cognitive flexibility levels decrease. In both academic and social life, awareness should be raised concerning the level of cognitive flexibility in stressful situations, and health behaviors towards coping with stress should be gained.