Objectives: Rose varieties are cultivated worldwide for ornamental flowers and have been greatly valued in the cosmetics and medicinal applications. Medicinal preparations from the different parts of the rose, including leaves, petals, and fruits, have been studied for various health benefits. Here, we have studied the efficacy of a standardized rose petal extract using the experimental models. Materials and Methods: The anti-obesity effect of a polyphenol-rich extract from the petals of Rosa multiflora var. platyphylla (RoseFit, 2%–3% isoquercetin) was studied using in vitro adipocyte differentiation model and in vivo diet-induced obesity model. Results: Treatment with 250 and 500 μg of rose fit dose-dependently reduced the differentiation of 3T3-L1 adipocytes and lipid accumulation thereof. The expression of adipogenic markers such as CCAAT/enhancer-binding protein-alpha and peroxisome proliferator-activated receptor gamma was markedly down regulated in the adipocytes treated with RoseFit. A 6-week treatment of high-fat diet (HFD) fed mice with RoseFit (100 mg and 200 mg/kg) significantly reduced the body weight, liver and fat pad weights, and adipocyte cell size of epididymal fat. Rose fit treatment also mitigated the hepatic inflammation significantly as compared to untreated HFD mice. Conclusion: Collectively, our findings suggest that the standardized rose petal extract may be used as a functional ingredient in food to increase the nutritional value and health-promoting effects.