To investigate the effects of 5-aminolevulinic acid photodynamic therapy on serum interleukin-6, interleukin-21, interleukin-23 and T cells 17/regulatory T cell balance in moderate to severe acne patient. 70 patients with moderate to severe acne who visited our dermatology outpatient clinic from January 2023 to August 2023 were selected as the research object and were divided into the experiment group (n=35) and the control group (n=35); the experiment group were treated with 5-aminolevulinic acid-based photodynamic therapy, while the control group was given 1 mg/bid isotretinoin capsules. The patients of the two groups were treated for 6 w; enzyme-linked immunosorbent assay to detect the serum interleukin-6, interleukin-21 and interleukin-23 level. Flow cytometry to detect the percentage of helper T cells 17 and regulatory T cell. Statistical Package for the Social Sciences software to analyze the spearman correlation between interleukin-6, interleukin-21, and interleukin-23 level with T cells 17/regulatory T cell balance. There were no statistical difference in the comparison of general information between the experiment and control groups (p>0.05). The therapeutic effect of the experiment group was more than the control group (p<0.05). Before treatment, serum interleukin-6, interleukin-21, and interleukin-23 levels have no statistical difference (p>0.05) between the two groups. After treatment, there were no statistical difference in serum interleukin-6, interleukin-21 and interleukin-23 levels (p>0.05). Serum interleukin-6, interleukin-21 levels were positive correlation with regulatory T cell/T cells 17 balance, while interleukin-23 levels were negative correlation with regulatory T cell/T cells 17 balance. Serum interleukin-6, interleukin-21, interleukin-23 level and peripheral blood T cells 17/regulatory T cell balance were associated to the therapeutic effect of moderate and severe acne patients after treatment. 5-aminolevulinic acid-based photodynamic therapy significantly improved the therapeutic effect of moderate and severe acne, but had no effect on serum interleukin-6, interleukin-21, interleukin-23 and peripheral blood T cells 17/regulatory T cell balance.