Protein arginine methylation plays a crucial role in signal transduction, protein-protein interactions, and transcriptional regulation. Previously, we showed that protein arginine methyltransferase activity increased significantly during rat liver regeneration. In the present study, in vivo arginine methylation during liver regeneration was investigated. The presence of symmetric or asymmetric dimethylarginine in proteins varied significantly at the early stage of regeneration after partial hepatectomy. The nature of the 31 proteins that showed significant variations in arginine methylation were identified using 2-DE and MS. Many of these proteins were oxidative stress-related or oxidation-prone proteins that exhibited significant variations in arginine methylation without changes in their expression levels. The oxidation of some of the oxidation-prone proteins under oxidative stress such as carbonic anhydrase 3 decreased with increased levels of arginine methylation, whereas normal levels of protein oxidation were recovered as arginine methylation subsided. Taken together, this study demonstrated that time-dependent methylation events in hepatocytes during the early period of rat liver regeneration may participate in the regulation or protection of protein activities, thus presenting a significant new insight into the biology of proliferating cells at the post-translational modification level and into a key population of proteins involved in these processes.