A positive resist composition comprising (A) a resin comprising at least one kind of acrylate derivative repeating units, repeating units having lactone structures and repeating units having hydroxy group-substituted adamantane structures, having a glass transition temperature in the range of 70 to 155.degree. C. and capable of increasing its solubility in an alkali developer under action of an acid, (B) a compound capable of generating an acid upon irradiation with an actinic ray or radiation, and (C) an organic solvent.