Objective? To explore the correlation between mental workload and psychological capital among intensive care unit (ICU) nurses. Methods? From December 2016 to January 2018, we selected 339 ICU nurses from 7 general hospitals in Shanghai as subjects by convenience sampling. Nurses were investigated with the National Aeronautics and Space Administration Task Load Index (NASA-TLX) and Psychological Capital Questionnaire (PCQ-24). The univariate analysis and multiple hierarchical regression were used to analyze the correlation between mental workload and psychological capital among ICU nurses. Results? Among ICU nurses, the total average score of mental workload and was (68.14±12.01) and the total score of psychological capital was (98.49±17.47) respectively. Pearson correlation analysis showed that there was a negative correlation between mental workload and psychological capital among ICU nurses (r=-0.462, P＜ 0.05). Multiple hierarchical regression analysis showed that psychological capital could independently predict the mental workload of nurses explaining 20.2% of the variance. Conclusions? The mental workload is negatively correlated with the psychological capital among ICU nurses. Nursing managers can improve psychological capital of ICU nurses by psychological capital training so as to reduce their mental workload.