Objective:To investigate the clinical effect of 5-aminolevulinic acid (ALA) photodynamic therapy (PDT) combined with CO 2 fractional laser on hypertrophic scars. Methods:From 2017 to 2019, 20 patients [17 males, 3 females, aged (24.4±4.24) years] with mandibular acne keloid in the Department of Dermatology of Air Force Medical Center, were treated with ALA-PDT combined with CO 2 fractional laser treatment, once a month, 3 times in total, and were followed up for 6 months. The efficacy, safety, and recurrence were evaluated by the Vancouver scar scale (VSS) score. Results:The effective rate was 100% after three treatments. The VSS score decreased significantly after the first treatment, and as the number of treatments increased, the VSS score further decreased. The first improvement after treatment was thickness and hardness. There was no recurrence during the 6-month follow-up. The main adverse reactions were pain, erythema and pigmentation.Conclusions:ALA-PDT combined with CO 2 fractional laser can be used as a new treatment for hypertrophic scars.