Objective: To investigate invitro antioxidant and invivo antitumor activity of the crude methanolic extract of Aponogeton undulatus (A.undulatus) (MAU) along with its various organic fractions. Methods: A. undulatus leaves were successively extracted using methanol (MAU) and then fractionated by chloroform, ethyl acetate (EAU) and water. The total antioxidant capacity, lipid peroxidation inhibition assay, 1, 1-diphenyl-2-picrylhydrazyl (DPPH) free radical scavenging assay and ferrous reducing power assessment were used to evaluate the antioxidant potential of the crude extract and its organic fractions. The invivo antitumor activity is evaluated against Ehrlich ascites carcinoma (EAC) cell bearing in Swiss albino mice. Results: EAU showed the highest antioxidant capacity as (175.80±0.41) mg/g, IC50 value of DPPH scavenging activity was (38.84±0.02) μg/mL and also exhibited maximum lipid peroxidation inhibition activity with the IC50 value of (42.52±0.32) μg/mL than other fractions. The results demonstrate that reducing power of the extract was concentration dependent. In addition, EAU was administered at 50, 100 and 200mg/kg body weight respectively to EAC cell bearing mice and a significant (P<0.05) decrease in tumor volume, packed cell volume and viable cell count and also increased the life span (17.52%, 42.53% and 62.05%). Hematological profiles were restored to normal levels in MAU treated mice as compared to EAC control mice. Conclusions: The results were found to be significant and confirmed that the A. undulatus has remarkable antitumor activity with antioxidant potential.