A photoresist composition comprising a resin having structural units represented by the following formulas (I), (II) and (III): wherein R1, R2, R3, R11, R12, R13, R21, R22 and R23 each independently represents hydrogen or an alkyl; one of R14, R15 and R16 represents an aliphatic hydrocarbon residue and the rest each independently represents hydrogen or an aliphatic hydrocarbon residue, or two or three of R14, R15 and R16 form a hydrocarbon ring; and R represents a group cleavable by an action of an acid; and the photoresist composition affords excellent resolution, excellent profile and wide focus margin even on a substrate provided with an organic anti-reflective film.