Background: Nurse to patient's ratio having great effect on quality of patients care provided especially patient's safety. Aim: This study aimed to determine the effect of nurse patient's ratio on patient‟s safety. Research design: descriptive, correlational research design was used. Setting: The study was conducted at Assiut Fever Hospital (Isolation, Hemodialysis and Health insurance units). Subject: 55 nurses were observed. Tools : Personal data sheet and patient's safety observational check list were used. Results: Nurses shortage appear in dialysis unit followed by health insurance unit and the highest percentage of shortage appear in isolation unit (53.4%, 61.5%, and 72%). Nurse patient's ratio have positive relation with nurses‟ application of general and medication safety standards in morning shift (0.748, 0.778) respectively. There is a positive relation between the nurse patient's ratio in evening shift (100%), but in night shift was (98.2%) for not met general patient safety standards and 100% for medication safety standards Conclusion: There were statistically significant differences between nurses‟ application of patient's safety standards dimensions and nurse patient's ratio in the three shifts Recommendation: Developing strategies to use nurse patient's ratio effectively and provide continuous training for nurses about national patient's safety standards.