To provide a manufacturing process for a polymer polyol by which the amount of coarse particles formed in the course of polymerization are reduced and a polymer polyol excellent in filtrability is obtained.

In the process for manufacturing a polymer polyol comprising continuously polymerizing (b) ethylenic unsaturated monomers in (a) a polyol and, as necessary, (d) a diluting solvent in the presence of (i) a radical polymerization initiator and in the presence or absence of (c) a dispersing agent, the concentration of dissolved oxygen measured by a sensor-type dissolved oxygen meter in (E) a liquid mixture consisting of (a), (b), (i) and, as necessary, (c) and/or (d), just before it is fed to the polymerization vessel is 5-120 ppm.