The present invention provides a polishing technique which enables polishing of silicon carbide, which is difficult to be polished, with high efficiency and high surface accuracy. The present invention relates to a polishing slurry for polishing a substrate, which comprises abrasive particles containing manganese oxide as a main component and in which the content of the abrasive particles is less than 10% by weight based on the polishing slurry. The polishing slurry of the present invention has a pH of preferably 7 or more. It is particularly preferable to use manganese dioxide as abrasive particles. The polishing slurry of the present invention is suitable for a substrate of silicon carbide.