Psoriasis is an autoimmune disease that is characterized by the appearance of lesions on the skin. The current treatment aims to control the symptoms. The efficacy of Stachytarpheta jamaicensis (L.) Vahl’s for autoimmune rheumatoid arthritis and systemic lupus erythematosus has been tested in animal models. The aim of this research was to evaluate the effect of the water extract of S. jamaicensis leaves on psoriasis model animal (male Balb/c mice) induced topically by imiquimod. The water extract of S. jamaicensis leaves is made by boiling. The animal was divided into groups: normal, control, methotrexate 0.2 mg/kgBW, the extract (doses 25, 50 and 100 mg/kgBW). The measured parameters were the Psoriasis Area and Severity Index (PASI) score and skin histopathology. The results showed that all doses of the extract could reduce the PASI score when compared to the control group. Histological results showed that there was a decrease in keratin growth in test animals that were given the extract. Extracts at doses of 25 and 50 mg/kgBW can reduce the thickening of keratin in the epidermis of the back and ears. It can be concluded that the water extract of S. jamaicensis leaf has the most effective activity to prevent psoriasis recurrence in the dose range of 25 and 50 mg/kgBW.Keywords: Psoriasis, Stachytarpheta jamaicensis leaf water extract, PASI, keratin, imiquimod