Aldose reductase (AR) is the key enzyme for the polyol pathway and responsible for sorbitol accumulation during the hyperglycemia. The present article focuses on the role of phenol, pyrogallol, hydroquinone, resorcinol, catechol, and phloroglucinol in in vitro inhibition of AR. For this purpose, AR was purified from the sheep kidney with 5.33 EU mg(-1) specific activity and 0.64% yield using several chromatographic methods. Various concentrations of the compounds were tested on in vitro AR activity. IC50 values were found for phenol, pyrogallol, hydroquinone, resorcinol, catechol, and phloroglucinol as 6.5, 1.13, 5.45, 2.21, 1.8, and 2.09 mM, respectively, and their K-i constant was calculated as 3.45 +/- 0.92, 0.96 +/- 0.28, 3.07 +/- 0.46, 1.59 +/- 0.43, 2.5 +/- 0.35, and 2.54 +/- 0.45 mM, respectively. Pyrogallol showed better inhibitory effect compared to the other compounds. The inhibition mechanisms of all compounds were noncompetitive. In the presents study, in vitro AR inhibition was examined by the phenolic compounds.