Objective To evaluate the effects of compound glycyrrhizin on the percentage of Th17 cells and expression of interleukin(IL)-17A in peripheral blood of patients with psoriasis vulgaris, and to explore their relationship with therapeutic effects. Methods A total of 30 patients with mild to moderate progressive psoriasis vulgaris were randomly and equally divided into two groups:group 1 treated with compound glycyrrhizin injection, antihistamines and topical drugs, group 2 treated with antihistamines and topical drugs. Twelve healthy human subjects served as the control group. Blood samples were collected from the patients 1 day before start of treatment and after 3 weeks of treatment, and from the control group. Flow cytometry and enzyme-linked immunosorbent assay (ELISA)were performed to determine the percentage of Th17 cells and expression level of IL-17A respectively in the peripheral blood samples. Results Before the treatment, the percentage of Th17 cells and expression level of IL-17A were both significantly higher in the two patient groups than in the control group (all P<0.05). After the treatment, group 1 showed significant decreases in the percentage of Th17 cells and expression level of IL-17A compared with those before the treatment (both P<0.05), while no significant differences were observed in group 2 between pre-and posttreatment IL-17A expression level or Th17 cell percentage (both P>0.05). Furthermore, both Th17 cell percentage and IL-17A expression were significantly different between the two patient groups after the treatment (both P< 0.05). Conclusion Compound glycyrrhizin may treat psoriasis vulgaris by regulating Th17 cell percentage and IL-17A expression in peripheral blood.