The present invention provides a polishing composition with which differences in height of a SiN film can be sufficiently removed.The present invention is a polishing composition for use in polishing a polishing object having a surface which is positively charged at a pH of less than 6, containing water, abrasive grains, and an anionic copolymer having a specific unit structure, and having a pH of less than 6, wherein the anionic copolymer has at least two acidic groups having different acidities.