OBJECTIVE: To evaluate the effectiveness of Xiaoyin Jiedu(XYJD) granules in the treatment of psoriasis vulgaris(PSV) in patients with a blood-heat pattern(BHP) in terms of Traditional Chinese Medicine(TCM). We also aimed to identify the possible underlying immunological mechanism.METHODS: Twenty-five PSV patients with BHP and ten normal controls were enrolled from January 1,2015 to December 31, 2016. Patients were randomly assigned to either the XYJD group(15 cases) or the placebo group(10 cases), in which patients were treated with XYJD granules or a placebo, respectively. Additionally, albolene was used to relieve skin dryness in these two groups. The psoriasis area and severity indexes, dermatology life quality indexes and itching scores were assessed at the end of the 2 nd, 4 th and 8 th week of treatment. The number of peripheral blood T helper(Th) 9, Th17 and regulatory T cells(Tregs) and the m RNA and protein expression levels of PU.1, RAR-related orphan receptor(ROR)-γt, forkhead box protein 3(Foxp3), interleukin(IL)-9, IL-17, IL-23 and IL-10 in the control and experimental groups were compared before and after treatment.RESULTS: Psoriasis area and severity indexes and itching scores of patients in the XYJD group were significantly lower than those in the placebo group,whereas dermatology life quality indexes were significantly higher. In comparison with the placebo group, XYJD granules significantly reduced the number of Th17 cells and the m RNA and protein expression levels of Th17-related ROR-γt, IL-17, IL-22 and IL-23 in the peripheral blood and reduced the number of Th9 cells and the m RNA and protein expression levels of Th9-related PU.1 and IL-9.CONCLUSION: XYJD granules were effective against PSV in patients with BHP by reducing the number of Th9 and Th17 cells and the levels of their related cytokines.