Abstract: Objective To compare the effects of photodynamic therapy with 5- amino-ketovalic acid at different concentrations on skin physiological indexes and efficacy in treating moderate to severe acne. Methods A total of 88 patients with moderate and severe acne were divided into control group(n=44)and observation group(n=44). The control group was treated with photodynamic treatment of 5-amino-ketovalic acid at a concentration of 5.0%, while the observation group was treated with photodynamic treatment of 5-amino-ketovalic acid at a concentration of 10.0%. The clinical efficacy, skin physiological indexes and Acne Scoring System(GAGS)scores of the two groups were compared. Results The effective rate in the observation group was significantly higher than that in the control group(P<0.05); after treatment, the water content of the two groups increased, and the oil content and pH value decreased compared with the treatment before(P<0.05), there were no significant differences in the water content and pH value between the two groups(P>0.05). The oil content of skin in the observation group was lower than that of the control group(P<0.05). The GAGS scores of the two groups decreased gradually at the first and third weeks of treatment(P<0.05), and the GAGS scores of the observation group were lower than those of the control group at the above time points(P<0.05). Conclusion Photodynamic therapy with 5-amino-ketovalic acid at a concentration of 10.0% has significant clinical efficacy and higher safety in the treatment of moderate to severe acne, and can obviously improve sebum secretion of patients.