Background The wide proliferation of Covid-19 has impacted billions of people all over the world. This catastrophic pandemic outbreak and ostracism at work have posed challenges for all healthcare professionals, especially for nurses, and have led to a significant increase in the workload, several physical and mental problems, and a change in behavior that is more negative and counterproductive. Therefore, leadership behaviors that are moral in nature serve as a trigger and lessen the adverse workplace effects on nurses’ conduct. Aim (...) this research is directed to explore the impact of post-COVID-19 workplace ostracism on nurses’ counterproductive behavior and examine the role of moral leadership as a mediating factor in post-COVID-19 workplace ostracism and nurses’ counterproductive behavior. Ethical consideration Ethical review and approval Was received from Ethical Committee at the Faculty of Nursing, Alexandria University, Egypt. Methods A cross-sectional and correlation study was implemented in all units of medical, surgical, critical and intensive care units by using three tools; moral leadership questionnaire, Workplace Ostracism Instrument (WOS), and Counterproductive Work Behaviors Questionnaire (CWBs). A convenient sample of 340 from 699 bedside nurses was granted. Results This study revealed that nurses’ perceived moderate mean percent (55.49 ± 3.46) of overall workplace ostracism and counterproductive behavior (74.69 ± 6.15). However, they perceived a low mean percentage of moral leadership. There was a significant positive correlation between workplace ostracism and counterproductive behavior. Otherwise, a significant negative correlation was found between moral leadership, workplace ostracism and counterproductive behavior. Also, this study proved the mediating effect of moral leadership in decreasing workplace ostracism by 79.3% and counterproductive behavior by 36.7%. Conclusion Hospital administrators need to be aware of the significance of moral leadership and apply integrity in the clinical setting to reduce the drawback of isolation on nurses' conduct and increase value for the organization as a whole and nurses in particular. (shrink)