Natural phenolic acids are commonly present in plants consumed in the diet. Recently we have observed that different natural phenolic acids exert differential effects on the body mass gain in ovariectomized and non-ovariectomized female rats. The aim of the present study was to investigate the effects of ferulic, caffeic, p-coumaric and chlorogenic acids on serum estradiol and total cholesterol levels in ovariectomized and non-ovariectomized rats. The experiments were carried out on 3-month old female Wistar Cmd:(WI)WU rats, divided into following groups (n=8 in each group): non-ovariectomized control rats and non-ovariectomized rats receiving ferulic, caffeic, p-coumaric or chlorogenic acids, sham-operated control rats, ovariectomized control rats and ovariectomized rats receiving the same phenolic acids. The phenolic acids were administered at a dose of 10 mg/kg p.o. daily for 4 weeks. Serum estradiol and total cholesterol levels on the next day after the last administration of the phenolic acids were examined. The phenolic acids did not affect serum estradiol or total cholesterol levels in non-ovariectomized rats. In ovariectomized rats, caffeic acid and to a lesser extent p-coumaric acid increased serum estradiol level, which effect correlated with a decreased body mass gain. All the phenolic acids decreased serum cholesterol level in ovariectomized rats. Concluding, the anti-obesity activity of some phenolic acids may be, at least partially, connected with estrogenic pathways.