To provid a high sensitivity and high resolution practical resist compsn. using a polymer having high transmittance to far UV of ≤220 nm, in particular ArF excimer laser light and excellent in etching resistance and to provide a pattern forming method using the resist compsn.

This resist compsn. contains a polymer contg. monomeric units represented by formula as the constituent units, a photosensitive compsn. that generates an acid when exposed and a solvent capable of dissolving them. In the formula, X is a polycyclic hydrocarbon group that may have a substituent, Z is a spacer or a bonding radical and R is a substd. alkyl or alkenyl group having one or two protected hydroxyl groups.