Obesity and its related complications are one of the world’s alarming preventable causes of tumor , diabetes and cardiovascular diseases. Whereas, medicinal herbs are potential source of therapeutic drugs. The present study was focused on bioactive secondary metabolites of methanolic extract from whole plant Hartmannia rosea G. Don. The new compound(1), quercetin 3-O-β-Dallopyranoside- 3″, 6″- diacetate (1), and two known compounds, ursolic acid (2) and gallic acid (3), were isolated for the first time from Hartmannia rosea G. Don. The structure of isolated new compound (1), quercetin 3-O-β-D-allopyranoside- 3″, 6″- diacetate was elucidated by using chromatographic and modern spectroscopic techniques. The cytotoxic activity, anticancer and anti- obesity effects of compound (1) were evaluated against normal ,(3T3-NIH) and Human Pancreatic cancer cell line (PSN-1). The anti- adipogenic effect on 3T3-L1 cell line was also evaluated. The tested compound (1) showed no cytotoxicity against normal cells (3T3-NIH) but has moderate activity against PSN-1 (Human Pancreatic cancer cell line) at a higher dose. However, it showed a pronounced inhibitory effect against adipogenesis of 3T3-L1 adipocytes. The inhibition of the formation of mature adipocytes indicated that quercetin 3-O-β-D- allopyranoside- 3″, 6″-diacetate (1) from Hartmannia rosea G. Don. has potential anti-obesity effects and may be a better alternate of chemical and biochemical agents used to control obesity and related chronic diseases. However its exact mode of action will further be undertaken.