Provided are: a method for producing a resin, whereby it becomes possible to produce a resin that enables the formation of a resist film having excellent resolution and also enables the reduction in scums during the formation of a pattern; and a method for producing an active ray-sensitive or radiation-sensitive composition. The method for producing a resin comprises: a first step of producing a resin containing a repeating unit represented by general formula (1) and a repeating unit containing a group capable of generating a polar group upon being decomposed by the action of an acid, therebyproducing a resin precursor containing a repeating unit represented by general formula (2) and a repeating unit containing a group capable of generating a polar group upon being decomposed by the action of an acid; and a second step of deprotecting a group represented by -OY in the repeating unit represented by general formula (2) in the resin precursor with an acid or a base to produce a repeating unit represented by general formula (1).