Background: Patients who undergo bone marrow transplantation experience a sequential suppression of host defenses, resulting in varying infectious risk at different phases of the transplantation process, so such group of patients are at increased risk for contracting infectious diseases (covid-19) with high morbidity and mortality rates. Aim of study was to assess staff nurses compliance with covid-19 preventive measures during caring of patients with bone marrow transplantation and its affecting factors. Design: A descriptive exploratory design was utilized to achieve the aim of the study. Setting: The present study was carried out in the bone marrow transplantation unites at two settings, Dar El Salam oncology center and Naser institute hospital. Study subjects: A convenient sample of all available staff nurses (n=50),25 nurses in each selected setting. Tools: I. Nurses' self-administered questionnaire, it included demographic characteristics, knowledge assessment & factors influencing compliance: II - Nurses' practice observational checklist. III. Nurses' attitude Likert scale and V. Nurses compliance assessment scale. Result: revealed that (56%) of studied nurses had good level of knowledge, (30%) of them had average level of knowledge and (14%) of them had poor level of knowledge regarding COVID -19 preventive measures, 74% of the studied nurses reported low affecting factors, 14% of them reported moderate affecting factors and 12% of them reported high factors affecting their compliance with COVID-19 preventive measures. As well , (58%) of studied nurses had high competency level of practice, (26%) of them had moderate competency level and (16%) of them had low competency level regarding covid-19 preventive measures during caring of patients with BMT. Besides, (64%) of the studied nurses had positive attitude, (36%) of them had negative attitude. Regarding nurses compliance, (56%) of them had high level of compliance, (26%) of them had moderate level of compliance and (18%) of them had low level of compliance. Conclusion: more than two quarter of the studied nurses had good level of knowledge, half of them had good competency level of practice and more than half of them had positive attitude. Also, more than half of them had high level of compliance. And more than three quarters of them reported low factors affecting their compliance with Covid-19 preventive measures during caring of patients with bone marrow transplantation. Additionally, there was highly statistically significant positive correlation between the studied nurses total level of knowledge, practice, attitude, affecting factors and their compliance with COVID-19 preventive measures. Recommendation.Importance of continuous inservice training program for nurses staff regarding covid-19 preventives measures during caring of patients with bone marrow transplantation t taking into consideration the studied affecting factors to improve their performance and consequently  their compliance .