The aim of the study was to evaluate the influence of a prolonged administration of two natural compounds – resveratrol (20 ppm) and protocatechuic acid (2000 ppm) – on the health status of Wistar rats. The animals were kept on supplemented diets for 7 and 24 weeks. Body weight was assessed weekly, and liver weight during autopsy. Liver morphology was evaluated histologically. The body weight in the 24th week, body weight gain (between the 1st and the 24th week of the experiment), and liver weight were significantly higher for the animals kept on the diet including resveratrol throughout the experiment than for those that had received this diet during the initial 7 weeks. However, differences in these parameters, as well as in the relative liver weight, between the control group and the groups exposed to both compounds were insignificant. Occasionally, mild, mostly reversible, microscopic hepatic changes (i.e., hydropic and fatty changes) were found, and these were slightly more common in the groups kept on supplemented diets. It seems that resveratrol and protocatechuic acid did not significantly disturb the wellness of rats, even after prolonged exposure.