Peroxisome proliferator-activated receptor α (PPARα) is a member of the steroid hormone receptor superfamily and is well known to act as the molecular target for lipid-lowering drugs of the fibrate family. At the molecular level, PPARα regulates the transcription of a number of genes critical for lipid and lipoprotein metabolism. PPARα activators are further shown to reduce body weight gain and adiposity, at least in part, due to the increase of hepatic fatty acid oxidation and the decrease in levels of circulating triglycerides responsible for adipose cell hypertrophy and hyperplasia. However, these effects of the PPARα ligand fenofibrate on obesity are regulated with sexual dimorphism and seem to be influenced by the presence of functioning ovaries, suggesting the involvement of ovarian steroids in the control of obesity by PPARα. In female ovariectomized mice, 17β-estradiol inhibits the actions of fenofibrate on obesity through its suppressive effects on the expression of PPARα target genes, and these processes may be mediated by inhibiting the coactivator recruitment of PPARα. Thus, it is likely that PPARα functions on obesity may be enhanced in estrogen-deficient states.