The invention provides a positive photoresist composition which exhibits a high level of etching resistance and attains high resolution, and enables the formation of a fine pattern using an electron beam exposure step, as well as a method for forming a resist pattern that uses the positive photoresist composition. This positive photoresist composition for use with EB contains a resin component (A) that exhibits increased alkali solubility under the action of acid, an acid generator component (B) that generates acid on exposure, and an organic solvent (C), wherein the component (A) comprises a copolymer containing a first structural unit (a1) derived from hydroxystyrene and a second structural unit (a2) derived from a (meth)acrylate ester having an alcoholic hydroxyl group, and a portion of the hydroxyl groups of the structural units (a1) and the alcoholic hydroxyl groups of the structural units (a2) are protected with acid dissociable, dissolution inhibiting groups.