Abstract: Macromers having a poly (ethylene glycol) central block, extended with poly (ε caprolactone) and terminated with diacrylate, were synthesized. Biodegradable hydrogels can be formed by photopolymerization in an aqueous solution using UV irradiation. The structure of the hydrogels, their gel content and swelling ratio etc. were characterized. It is shown that using nontoxic photoinitiators, the macromers can rapidly photopolymerize in water, and the dried gel absorbs water in very short time to give a large swelling ratio. The swelling properties can be controlled by changing the PEG chain lengths or mixing the different molecular weight of macromers. These novel biodegradable materials are suitable for use in macromolecular controlled delivery of medicines.