A method for producing a resist copolymer having a weight-average molecular weight of not less than 3000 and not more than 6000, in which copolymer the contents of an oligomer having a molecular weight of not more than 1000 and a byproduct derived from a polymerization initiator are small, is provided.The method for producing a resist copolymer comprises the step of continuously supplying a solution containing a monomer and a solution containing a polymerization initiator to a heated solvent to carry out a radical polymerization, wherein the variation range of the concentration of the polymerization initiator in polymerization solution is within ±25% of the median value between the maximum concentration and the minimum concentration during specific time; and the variation range of the concentration of unreacted monomer in the polymerization solution is within ±35% of the median value between the maximum concentration and the minimum concentration during specific time.