OBJECTIVE：To observe the efficacy and safety of Isotretinoin erythromycin gel in the treatment of mild-to-moderate acne vulgaris. METHODS： 120 patients with mild-to-moderate acne vulgaris were randomly divided into observation group and control group. Observation group was given appropriate amount of Isotretinoin erythromycin gel in affected areas every night before bed， once a day； control group was given appropriate amount of Viaminate vitamin E cream in affected areas every night before bed， once a day. The skin was thoroughly cleaned before treatment， no cosmetics and no spicy diet， rest rules and less staying up late. The treatment course for both groups was 2 months. Clinical efficacy， skin lesion scores， inflammation sebum secretion rate （SER） before and after treatment， and the incidence of adverse reactions in 2 groups were observed. RESULTS： The total effective rate in observation group was significantly higher than control group， the difference was statistically significant（P＜0.05）. after treatment， the skin lesion scores and SER in 2 groups were significantly lower than before， the number of skin lesions， rash forms and SER in observation group were significantly lower than control group， the differences were statistically significant （P＜0.05）； but there was no significant difference in the rash types between 2 groups （P＞0.05）. And there was no significant difference in the incidence of adverse reactions（P＞0.05）. CONCLUSIONS： Isotretinoin erythromycin gel has significant efficacy in the treatment of mild-to-moderate acne vulgaris， with good safety.