An object of the present invention is to provide a high-performance polymer dispersant that can be applied to cellulose being a hydrophilic substance, and another object of the present invention is to provide a technology for practical application of obtaining a cellulose-dispersed resin composition that realizes stable dispersion of cellulose in a simpler manner and in an environmentally conscious manner that never uses a large amount of organic solvents when the polymer dispersant for cellulose is applied to cellulose and disperses the cellulose in a thermoplastic resin. These objects are achieved by providing a polymer dispersant for cellulose, being a polymer compound including a block copolymer structure having a resin-affinitive segment A and a cellulose-adsorptive segment B, the polymer compound synthesized by a reversible chain transfer catalyzed polymerization (RTCP) method not using any of a heavy metal, a nitroxide compound, and a sulfur-based compound, using an organic iodine compound as an initiation compound, and using a phosphorus compound, a nitrogen compound, an oxygen compound, or a carbon compound as a catalyst.