Psoriasis is an autoimmune disease that occurs in the skin. An example of a drug that can induce psoriasis is imiquimod. This study aims to determine the effect of water extract of Stachytarpheta jamaicensis L. Vahl. leaves on haematological profile, spleen organ index and spleen histology in male Balb/c mice induced imiquimod. The extract was made by boiling water. The animals divided into 6 groups: normal, control, methotrexate 0.2 mg/kg BW, the extract at doses of 25, 50 and 100 mg/kg BW. Measurement of the haematological profile was carried out in the end of the srudy and the parameters were white blood cells, lymphocytes, mid-sized cells (MID), granulocytes, red blood cells, haemoglobin, haematocrit and platelets. The results showed that the extract at all doses can increase white blood cells including lymphocytes, MID, granulocytes, red blood cells, haemoglobin, haematocrit and platelets compared to control group (p<0.05). The result also showed that the extract at all dose can prevent enlargement of the spleen and reduce the level of lymphocyte infiltration in the spleen. It can be concluded that the water extract of S.jamaicensis leaves affects the haematological profile and spleen organ on animal induced imiquimod.