The present invention provides a chemically amplified resist composition comprising: (A) a resin which comprises (a) a structural unit having an acid-labile group, (b) a structural unit having at least one hydroxyl group, (c) a structural unit having at least one lactone structure, and (d) a structural unit represented by the formula (Ia) or (Ib): ##STR00001## wherein R.sup.1 represents a hydrogen atom or a methyl group, R.sup.3 represents a methyl group, n represents an integer of 0 to 14, and Z represents a single bond or --[CH.sub.2].sub.k--COO--, and (B) at least one acid generator.