Background: Shoulder pain, disability and impaired movements are frequently reported complication in post- mastectomy patients. Most individuals who have had a mastectomy suffer from adhesive capsulitis, which causes shoulder pain and impairment. Aim: The current study was conducted to investigate the effectiveness of Muscle energy technique (MET) on shoulder adhesive capsulitis post mastectomy. Patients and methods: The present work was carried-out on sixty patients with adhesive capsulitis after mastectomy who participated in this study, they were aged from 40 to 60 years. The individuals were recruited from National Cancer Institute, Cairo University. They were randomized into 2 groups; every group included 30 patients. Group (A) (study group): were givenMET5 days per week for eight weeks as well as their traditional physiotherapy program (Mobilization exercises, stretching of the Posterior capsule, as well as Range of motion (ROM) exercises). Group (B) (control group):received only the conventional physical therapy program, 5 days per week for eight weeks. Visual analogue scale (VAS) was utilized to measure the shoulder pain. Goniometer was utilized to evaluate shoulder ROM. Shoulder pain and disability index (SPADI) was utilized to evaluate shoulder function. All assessments were conducted pretreatment as well as post treatment. Results: In both Groups A and B, post-treatment VAS as well as SPADI scores were significantly lower than pre-treatment scores (p < 0.001). the percentage of change of VAS as well as SPADI in Group A was 68.28% and 71.88% respectively, while it was, 45.76% and 54.4% in group B respectively. In both groups, post-treatment shoulder flexion, abduction, as well as lateral rotation were all significantly higher than pre-treatment values. Shoulder flexion, abduction, as well as external rotation all increased by 128.25, 75.76, and 99.95% in group A, whereas they increased by 97.58, 59.9, and 89.38% in group B, respectively. Pretreatment comparisons showed no statistically significant differences among the groups. Post-treatment comparisons between the two groups showed that VAS and SPADI scores were significantly lower in Group A compared to Group B (p < 0.001). Shoulder flexion, abduction, as well as external rotation were significantly improved in group A than in group B after treatment (p < 0.001). Conclusion: adding MET in rehabilitation program can improve the shoulder pain, ROM as well as function in adhesive capsulitis management Postmastectomy.