A CMP polishing slurry of the present invention, contains cerium oxide particles, a dispersant, a polycarboxylic acid, a strong acid having a pKa of its first dissociable acidic group at 3.2 or less, and water, the pH of the polishing slurry is 4.0 or more and 7.5 or less, wherein the strong acid is contained 100 to 1,000 ppm or 50 to 1,000 ppm, or the strong acid is a monovalent strong acid contained 50 to 500 ppm or is a bivalent strong acid contained 100 to 1,000 ppm. The preferable polycarboxylic acid is a polyacrylic acid. The present invention allows polishing in the CMP methods of surface-smoothening an interlayer dielectric film, a BPSG film and a shallow-trench-isolation insulation film with high speed operation efficiently and easier process management and cause smaller fluctuation in film thickness due to difference in pattern density.