Objective To investigate the levels of psychological capital and post competency among critical care nurses, and to explore the influence of psychological capital on post competency. Methods A total of 254 intensive care unit (ICU) nurses were surveyed by using the Psychological Capital Questionnaire and a self-designed competency questionnaire for ICU nurses. Results The ICU nurses scored (90.50±17.75) on psychological capital and (140.92±42.28) on post competency, showing positive correlation between them (P<0.01). The dimensions of self-efficacy and optimism in psychological capital had significant impact on post competency of ICU nurses (P<0.01 for both). Conclusion ICU nurses reported moderate to high levels of psychological capital and post competency. Nursing managers should pay sufficient attention to psychological capital of ICU nurses, particularly in cultivation and development of self-efficacy and optimism.