Disclosed is a cerium oxide slurry which enables both decrease of polishing scratches and increase of polishing rate by reducing coarse particles contained in the slurry by maximizing the dispersibility of cerium oxide particles. Also disclosed is a cerium oxide polishing liquid and a method for polishing a substrate using such a cerium oxide slurry or cerium oxide polishing liquid. Specifically disclosed is a cerium oxide slurry containing cerium oxide particles, a dispersing agent and water. This cerium oxide slurry has a cerium oxide/dispersing agent weight ratio of 20-80. Also specifically disclosed is a cerium oxide polishing liquid containing such a cerium oxide slurry and an additive such as a water-soluble polymer.