Effects of methanolic extract (ME) of Cassia fistula seed on the growth of Ehrlich ascites carcinoma (EAC) and on the life span of tumor bearing mice were studied. ME treatment showed an increase of life span, and a decrease in the tumor volume and viable tumor cell count in the EAC tumor hosts. Cytological studies have revealed a reduction in the mitotic activity, and the appearance of membrane blebbing and intracytoplasmic vacuoles in the treated tumor cells. Improvement in the hematological parameters following ME treatment, like hemoglobin content, red blood cell count and bone marrow cell count of the tumor bearing mice have also been observed. The results of the present study suggest that ME of C. fistula seed has an antitumor activity.