A polymer is obtained from copolymerization of a unit having a carboxyl and/or phenolic hydroxyl group substituted with an acid labile group with a hydroxyphenyl methacrylate unit having one acyl, acyloxy or alkoxycarbonyl group. The polymer is useful as a base resin in a positive resist composition. The resist composition comprising the polymer is improved in contrast of alkali dissolution rate before and after exposure, acid diffusion control, resolution, and profile and edge roughness of a pattern after exposure.