Background and Objectives: This investigation describes the effect of low level laser therapy (LLLT) on treatment of post-mastectomy lymphedema.Materials & Methods: Eleven women with unilateral arm lymphedema were included in this study. Patients received laser or placebo irradiation (GaAs/Mustng 890 nm, fluence: 1 J/cm2) over the arm and axillary area as laser and sham groups, respectively.Results: Four patients in each group (laser or sham) completed the treatments. Changes in limb circumference, pain score, motility and heaviness of the affected limb and desire to continue the treatment in five sessions of follow up were measured and compared to pre-treatment status. Pain reduction in laser group was more than sham group except for the weeks 3 and 9.Conclusions: Our study showed that LLLT with the wavelength of 890nm may have effects on reduction of pain and circumference of lymph-edematous limb after mastectomy.