Abstract: The present invention provides a polishing composition used in a polishing process of a silicon wafer, which has an improved smoothness and is environment-friendly. The polishing composition for the silicon wafer of the present invention comprises a metal oxide, an alkaline substance and water, wherein the alkaline substance is guanidines. Another polishing composition for a silicon wafer of the present invention comprises an alkaline substance and water, wherein the alkaline substance is guanidines. These polishing compositions may further comprise a chelating agent. The metal oxide is preferably a cerium oxide or a silicon oxide. The present invention encompasses a polishing method using the above polishing composition and a kit for the above polishing composition.