High concentration silica slurry

High concentration silica slurry providing excellent polishing speed and accuracy without impurities contaminations is disclosed. The high concentration silica slurry has a silica concentration of more than 50 % by weight and viscosity of less than 1000 mPa.s, wherein a silica powder is dispersed in the solvent, the ratio (DL/DT) of an average particle size of the silica powder measured by a laser diffraction particle size distribution method (DL) and that by a TEM photography observation (DT) is less than 1.3, and the average primary particle size is from 0.08 mu m to 0.8 mu m. Preferably, the high concentration silica slurry having a silica concentration of from 70 % by weigh to 80 % by weight and the viscosity at the time of preparing of less than 800 mPa.s, wherein the impurity concentrations of silica powder are less than 1.0 ppm each of sodium and potassium, less than 1.0 ppm aluminum, and less than 5 ppm each of sulfur, nickel, chromium, and iron.