Background: Obesity is one of the most serious global health problems of the 21^st century and it is considered as a principal risk factor in the initiation of various non-communicable chronic diseases such as dyslipidemia, atherosclerosis, cardiovascular, non-insulin dependent diabetes mellitus. Objective: The current study was designed to evaluate the effect of Rosmarinus Officinalis L. extract (RE) on serum cholesterol, HDL, LDL, TG, glucose and insulin, as well as enzymatic activity of serum GPx, SOD and catalase, body weight, adiposity index and insulin resistance in high fat diet (HFD) fed rats. Materials and Methods: Forty adult male albino rats of local strain were randomized into four equal groups. The first group was fed on basal diet and received 0.2 ml distilled water daily by oral intubations and kept as control group. The second group was fed on basal diet and received RE (100 mg/kg body weight daily by oral intubations). The third group was fed on high fat diet and received 0.2 ml distilled water by oral intubations, and the fourth group was fed on high fat diet with RE (100 mg/kg body weight daily by oral intubations). Results: Rats fed HFD showed significant increase in body weight, body weight gain, adiposity index, serum cholesterol, LDL, TG, fasting glucose, fasting insulin and HOMA-IR, and significant decrease in serum HDL and GPx, SOD and catalase in comparison to control group. Rats fed HFD with RE showed significant decrease in body weight, body weight gain, adiposity index, serum cholesterol, LDL, TG, fasting glucose, fasting insulin, and HOMA-IR,  and significant increase in serum HDL, GPx, SOD and catalase in comparison to HFD group and showed significant increase in body weight, body weight gain, adiposity index, serum cholesterol, LDL, TG in comparison to control group. Rats fed basal diet with RE showed insignificant changes in comparison to control group. Conclusion: The administration of RE showed increased oxidative activities of serum SOD, GPx and catalase enzymes as well as improvement of lipid profile and decreased glucose, insulin, body weight, adiposity index, and insulin resistance in HFD fed rats.