Provided are a polishing method that can be commonly applied to different types of silicon substrates varying in resistivity as well as a polishing composition set used in the polishing method. The silicon substrate polishing method provided by this invention comprises supplying a first polishing slurry S1 and a second polishing slurry S2 to a silicon substrate to be polished, switching them in this order midway through polishing the silicon substrate. The first polishing slurry S1 comprises an abrasive A1 and a water-soluble polymer P1. The polishing removal rate of the first polishing slurry S1 is higher than that of the second polishing slurry S2.