Proton pump inhibitors (PPIs) are a group of drugs that is commonly prescribed worldwide. However, the use of PPIs is accompanied with acute kidney injury and chronic kidney disease by mechanisms not entirely known. In the present study, omeprazole administration was found to cause a rapid phosphorylation of ERK1/2 signaling cascade accompanied with an increase in cyclin B1expression in rat kidney. In addition, administration of omeprazole enhancedthe activity of A disintegrin and metalloproteinase-17 (ADAM-17) ane the phosphorylation ofepidermal growth factor receptor (EGFR).Interestingly, concomitant administration of the pharmacological inhibitor of EGFR, gefitinib along with omeprazole caused an almost complete reduction of the phosphorylation of EGFR and ERK1/2 induced by omeprazole. Moreover, omeprazole administration significantly increased lipid peroxidation and reduced superoxide dismutase (SOD) activity in rat kidney. Collectively, Omeprazole activates ERK1/2 signaling cascade that could be translated to an increase in the expression of the cell proliferation gene cyclin B1inreactive oxygen species (ROS)-dependent manner. These effects may contribute to omeprazole-mediated chronic kidney disease.