Abstract: Objective To study the ef fi cacy and safety of 5-aminolevulinie acid photodynamic therapy (5-ALA-PDT) for moderatesevere facial acne. Methods Eighty-two patients with moderate-severe acne were divided into treatment group and control group(41 in each group). Patients in treatment group were treated with 3.7% 5-ALA followed by red light irradiation with a photodynamic therapy device, once a week, for 3 weeks. Those in control group underwent red light irradiation, once a week, for 3 weeks. The patients were followed up 2 and 4 weeks, 3 and 6 months after treatment, during which the therapeutic effects in two groups were compared and the adverse effects were recorded. Results The total effective rate was signi fi cantly higher in treatment group than in control group 2 and 4 weeks, 3 and 6 months after 5-ALA-PDT (44.90% vs 12.20%, 63.41% vs 21.95%, 87.80% vs 33.33%, 92.68% vs 48.57%, P< 0.05). The therapeutic effect was better in treatment group than in control group and increased with the times of treatment (P< 0.05). The major adverse reactions in treatment group were local burning, pain and itching which relieved after treatment.Moderate local pigmentation in 8 patients, found in treatment group, completely disappeared 3 months after treatment. Conclusion The effect of 5-ALA-PDT is signi fi cant on moderate - severe acne with mild adverse reactions, and is thus a good treatment modality for moderate - severe acne.