Background: Effective collaboration between nurses and physicians is associated with patient safety and quality of care. The aim: assess nurse-physician collaboration and its relation to patients' safety climate in critical care units. Design: correlation research design was used. Setting: The study was conducted in critical care units at Benha University and Benha Teaching Hospitals. Sample: convenience sample consisted of 86 nurses and 68 physicians. Tools: two tools were used; Tool I: Collaborative Practice Scale: consists of two parts; (part 1): personal characteristics and (part 2): Collaborative Practice Scale to assess nurses and physicians collaboration behavior. Tool II: Patient safety climate questionnaire to assess nurses' and physician' perceptions regarding patient safety climate. Results: the nurses and physicians had a neutral level of collaborative behavior; the total level of nurses' collaborative behavior was higher (53.7%) than physicians' (52.9%). Also nurses and physicians had neutral perception regard patient safety climate. Nurses had higher percent regard patient safety climate (53.58%) than physicians (50.08 %). Conclusion: there was significant correlation between nurses-physician collaborative behavior and patient safety climate. Recommendations: conduct inservice program and workshop about team work and patient safety and development of an inter-professional collaborative environment to increase nurses’ performance as well as improve patient safety climate.