Context. The plant Citrus maxima Merr. (Rutaceae), commonly known as shaddock or pomelo is indigenous to tropical parts of Asia. The objective of present study is to evaluate the methanol extract of Citrus maxima leaves for its antitumor activity against Ehrlich's Ascites Carcinoma cell in Swiss albino mice. Experimental design. The antitumor activity of methanol extract of Citrus maxima leaves (MECM) was evaluated against Ehrlich Ascites Carcinoma (EAC) cell line in Swiss albino mice. 2 × 106 cells were inoculated in different groups of animals. MECM (200 and 400 mg/kg BW i.p.) was administered for nine consecutive days. On day 10th half the animals of different groups were sacrificed for determination of tumor and haematological parameters and the rest half were kept with sufficient food and water ad libitum for determination of increase in life span. Result and Discussions. Oral administration of the extract at the doses of 200 and 400 mg/kg significantly decreased tumor parameters such as tumor volume, viable tumor cell count and increased body weight, hematological parameters and life span in respect of the EAC control mice. Conclusion. Experimental design exhibits significant antitumor activity of the extract (MECM) in a dose dependant manner.