The invention provides a photosensitive resin which can readily form, through photo-crosslinking, a surface coating which has hydrophilicity and high bioadaptability; a photosensitive composition containing the photosensitive resin; and a photo-crosslinked structure obtained from the photosensitive composition.The photosensitive resin is represented by the following formula (1): ##STR00001## (wherein n represents a mean polymerization degree and is 5 or more; R.sub.1 and R.sub.2, which may be identical to or different from each other, each represent an alkylene group, an arylene group, an oxyalkylene group, or a single bond; each of X and Y represents a photosensitive unit represented by the following formula (2): ##STR00002## or either one of X and Y represents a photosensitive unit represented by the above formula (2) and the other represents an amino group; R.sub.3 represents a group selected from among the groups represented by the following formula set (3): ##STR00003## R.sub.4 represents a group selected from among the groups represented by the following formula set (4): ##STR00004## at least one of R.sub.3 and R.sub.4 has at least one azido group; and R.sub.5 represents a hydrogen atom, an alkyl group, an acetal-group-containing alkyl group, an aryl group, an aralkyl group, or a substituent containing a base-forming nitrogen atom).