Abstract: 5-Fluorouracil (5-FU) is one of the widely used chemotherapeutic drugs targeting various cancers including colon cancer, but its chemoresistance remains as a major obstacle in clinical settings. Towards this goal, we evaluated the in vivo efficacy of umbelliferone (UMB) with 5-flurouracil (5-fu) against 1, 2-dimethylhydrazine (DMH) induced colon carcinogenesis in rats. Rats were divided into seven groups of six rats each. Rats in group 1 received high fat diet and served as control, group 2 rats received high fat diet with DMH (20mg/kg body weight) once a week subcutaneously for the first 15weeks which represent the colon cancer bearing rats. Group 3 rats received umbelliferone via intragastric injection at a daily dose of 30mg/kg body weight for 30weeks every day. Groups 4–7 rats received high fat diet with DMH (20mg/kg body weight) as in group 2. In addition group 4 rats (initiation) received UMB starting 1week before 1st DMH injection and continued till the end of last DMH injection, group 5 rats (post-initiation) received UMB after 1 week of last DMH injection and continued till the end of the experimental period, group 6 rats (Entire period) received UMB throughout the experimental period. Group 7 cancer bearing rats received 5-flurouracil (100mg/kg body weight) once a week intravenously for first 4weeks and UMB was given as in group 6 throughout the experimental period of 30 weeks Levels of glutathione-s-transferase (GST), superoxide dismutase (SOD), catalase (CAT), and glutathione peroxidase (GPx), glutathione reductase (GR) and reduced glutathione (GSH) decreased following DMH treatment, and also the levels of lipid peroxidation end products like thiobarbituric acid substances (TBARS), lipid hydroperoxides (LOOH) and conjugated dines (CD) were significantly decreased in DMH-treated rats. Administration of UMB alone and combined effect of UMB with 5-Fu significantly reversed these activities to near normal, which concludes the anti-carcinogenic efficacy of UMB. This effect was further confirmed by histopathological studies and finally proved that UMB as an effective and potential chemotherapeutic agent against DMH-induced colon carcinogenesis. [Copyright &y& Elsevier]