Diazinon, an organophosphorus insecticide, is employed to control pests in agriculture. Diazinon may contaminate the environment during the manufacturing process or agricultural application. Previous studies have revealed that diazinon may induce alteration in the protein profile of the liver. Here, a proteomics approach was used to investigate the effects on the protein profile in the liver of rats of subacute oral exposures at 15 mg/kg of diazinon. Liver proteins were separated using 2D-PAGE, and stained by MS-compatible silver staining and/or the fluorescent SYPRO (R) Ruby protein gel stain. Gels were scanned and analyzed using the Image Master software. Differentially displayed protein species were identified using MALDI-TOF/TOF and MASCOT software. Significantly altered protein species were identified to be involved in apoptosis, cell metabolism, transport, and antioxidant systems. Exposure to diazinon decreased levels of some species of catalase, peroxiredoxin-6, 3-ketoacyl-CoA thiolase, and glucose regulated protein78, whereas the level of protein disulfide-isomerase A3 increased. Our results suggested that diazinon may induce hepatotoxicity through oxidative stress, apoptosis, and metabolic disorders in rat liver.