Background: Most nurses who are working with intensive care and psychiatric patients accept psychological talents and skills as mental toughness and rejection sensitivity that affect their work performance. Aim: To determine the association of mental toughness, rejection sensitivity, and work performance among staff nurses working at intensive care unit and psychiatric unit. Setting: This study was conducted at Medical Intensive Care Unit (MICU) as a group I and Inpatient's Unit of the Psychiatric as group II. Subjects: The study subjects were composed of simple random sample of nurses (n=100) who working at the two settings. Tools: Three tools were used,   Tool I: Mental Toughness Questionnaire, Tool II: Rejection Sensitivity Questionnaire, and Tool III: Nursing Work Performance Observational Checklist. Results: Majority (91.5%) of group II obtained an average level of mental toughness and rejection sensitivity compared to (54.7% and 81.1%) of group I respectively. The total mean of nurses' responses about work performance all were at moderate level Mean±SD(2.699±10.930) for group I compared to group II Mean±SD(2.368±9.081). Conclusion: There were neither associations nor correlations between mental toughness, rejection sensitivity levels and work performance levels among staff nurses working at intensive care unit and psychiatric unit nursing groups. Recommendations: Conducting educational training program for nurses at two units about mental toughness and rejection sensitivity and maintaining the periodical orientation of nurses at two units about work performance dimensions.