Background: People who had a mastectomy may feel pain that comes from the breast that was cut off. These are called phantom breast sensations (PB sensations) and phantom breast pain. Some of the problems that breast cancer patients have after treatment are a limited range of motion in the shoulder, arm swelling, loss of shoulder strength and PB feeling. Purpose: To investigate efficacy of low-level laser therapy on shoulder mobility and phantom breast pain postmastectomy. Patients and methods: 44 patients with postmastectomy phantom pain, their ages ranged from 20 to 50 years. They were randomly divided into two groups;Group (A) (study group): received low level laser therapy combined with routine physical therapy exercises, 3 sessions per week for 4 weeks, Group (B) (control group):  received only routine physical therapy exercises, 3 sessions per week for 4 weeks. Visual analogue scale (VAS) was used to measure shoulder pain, goniometer was used to measure shoulder range of motion. Quality of life questionnaire was used to assess functional state and symptoms. Results: There was a significant decrease in VAS post treatment compared with that of pretreatment in study group when compared with control group. Statistical analysis showed significant improvement in shoulder flexion, abduction and external rotation post treatment compared with that of pretreatment in both groups. Statistical analysis showed significant improvement in quality-of-life questionnaire post treatment compared with that of pretreatment in both groups. Conclusion: Low level laser therapy can improve shoulder ROM, quality of life scale and decrease phantom pain postmastectomy.