Receptor-like kinases (RLKs) are important for plant growth, development and defense responses. The S-receptor protein kinases (SRKs), which represent an RLK subfamily, control the self- incompatibility among Brassica species. However, little information is available regarding SRK functions in rice. We identified a gene OsSRK1 encoding an atypical SRK. The transcript of OsSRK1 was induced by abscisic acid (ABA), salt and polyethylene glycol. OsSRK1 localized to the plasma membrane and cytoplasm. Leaf width was increased in OsSRK1-overexpression (OsSRK1-OX) transgenic rice plants, likely because of an increase in cell number per leaf. Furthermore, the expression levels of OsCYCA3-1 and OsCYCD2-1, which encode positive regulators of cell division, were up-regulated in leaf primordium of OsSRK1-OX rice plants relative to those in wild type. Meanwhile, the expression level of OsKRP1, which encodes cell cycle inhibitor, was down-regulated in the OsSRK1-OX plants. Therefore, it is deduced that OsSRK1 regulates leaf width by promoting cell division in the leaf primordium. Additionally, OsSRK1-OX plants exhibited enhanced ABA sensitivity and salt tolerance compared with wild type. These results suggest that OsSRK1 plays important roles in leaf development and salt responses in rice. Keywords: rice, S-receptor-like protein kinase, OsSRK1, salt tolerance, leaf width, cell division