Background: Upper limb impairments are very common and impact self-reported function following breast cancer surgery with dissection of axillary lymph nodes. Restoring arm function on the affected side after mastectomy is a key nursing goal, through instructing performance of exercises immediately after surgery. Aim of the study was to evaluate the effect of early post mastectomy exercises program for women on their upper limb function. Methods: Quasi-Experimental design was utilized in this study, included a sample of 70 women scheduled for mastectomy with axillary lymph node dissection throughout a period of three months in surgical departments at Benha University Hospital, Benha Teaching Hospital and National Cancer Institute of Cairo University, were randomly divided into study and control groups to collect the data over a period of one year. Tools of data collection used: Structured Interviewing Questionnaire Sheet, Subjective Outcome Questionnaires for Upper Limb Function, including (Brief Pain Inventory, & Disabilities of the Arm, Shoulder, and Hand (DASH) questionnaires), and Objective Outcome Measures, including (Shoulder Range of Motion, Upper Extremity Circumferential Measurement, & Grip Strength of Hands). Results indicated that there were highly statistically significant differences between both study and control groups at the end of study period regarding mean knowledge, subjective and objective outcome measures of upper limb function, but with minimal evidence of lymphedema among studied group. Conclusion: The results showed the effectiveness of early postmastectomy exercises program on improving knowledge, and outcome measures for upper limb function after mastectomy. The study recommended the need of knowledge after discharge, so planned pre discharge education should be prepared and given to women as well as systemic education during follow up. Stressing the importance of attending early postoperative exercises and complying with them for at least 6 months after mastectomy. Focusing on early assessment and diagnosis of arm lymphedema from physicians and nursing staff.