A photosensitive composition comprising: an acid-decomposable compound having at least one substituent which is decomposed by an acid, forming a product which reacts with alkali solution and forms --COO.sup.- or --SO.sub.3.sup.- ; and a compound which generates an acid when exposed to a chemical radiation. If necessary, the composition further comprises an alkali-soluble polymer. The acid-decomposable compound is one which is represented by the following formula (1), and the alkali-soluble polymer has a softening point of 150.degree. C. or more and an average molecular weight of 3000 to 8000. When used as photoresist, the composition can form a fine resist pattern. ##STR1## where R.sub.1 and R.sub.2 are either the same or different, each of which represents at least one selected from the group consisting of hydrogen, halogen atom, cyano group, nitro group, silyl group, and monovalent organic group; X represents >C.dbd.O or --SO.sub.2 --; Y represents a divalent organic group; R.sub.1 and R.sub.2 can be bonded together, forming a ring; and at least one of R.sub.1, R.sub.2, and Y has a substituent which is decomposed by an acid.