Opuntia humifusa contains high levels of antioxidants including vitamin C, flavonoids and polyphenols, which may provide beneficial effects such as hypolipidemic activity and the reduction of atherosclerosis in postmenopausal women. This study was conducted to determine if the intake of O. humifusa seeds powder (OHS) regulates lipid concentrations, glutamate-oxaloacetate transaminase (GOT), and glutamate-pyruvate transaminase (GPT) in the serum of ovariectomized rats. Sprague-Dawley female rats were randomly assigned to either a sham-operated group (Sham) or one of the following four ovariectomy (OVX) subgroups: OVX with vehicle (OVX), OVX with 100, 200, and 500 mg/kg/day OHS (OHS100, OHS200, OHS500). Daily oral administration of OHS was initiated one week after ovariectomy and continued for seven weeks. Upon completion of treatments, organs were weighed and GOT, GPT, total cholesterol (TC), low-density lipoprotein cholesterol (LDL-C) and high-density lipoprotein cholesterol (HDL-C) levels were determined enzymatically. No significant differences in feed intake and organ index were observed among the groups. Significant decreases in GPT, TC and LDL-C (p<0.05) were observed in all of the OHS groups (OHS100, 200 and 500), while no significant changes in HDL-C were observed. In addition, the OHS200 and OHS500 treatment groups exhibited a lower level of serum GOT compared to the OVX group. These results indicate that supplementation with O. humifusa seeds could induce favorable changes in serum lipoprotein and lipid profiles, which frequently worsen with inadequate estrogen availability.