Protocatechuic acid treatment inhibited the activation of polyol pathway by reducing the activities of aldose reductase and sorbitol dehydrogenase and increasing the activity of glyoxalase I. The reduction of AGEs production in protocatechuic acid treated T2D rats would be correlated with its effect on polyol enzymes. The gene discussed is AKR1B1; the disease is type 2 diabetes mellitus.