The biodegradation behavior in vitro and in vivo of polycaprolactone poly (ethylene oxide) block copolymers ( P C E) has been reported in detail. Photodegradation testof P C E was performed by exposure to U Vlight. The mechanical properties and the inherentviscosity of P C Esamples which are subjected to photodegradation were determined . Thephotodegradation rate of P C E was much more faster than its hydrolysis rate and wasincreased with increasing poly(ethylene oxide) content. The experimental results alsoindicated that the pure poly(ethylene oxide) ( P E O) can not be photodegraded alone. Amechanism forthe photodegradation of P C Ecopolymers was proposed :thecarbonylgroupsin P C Lsegmentscatalyze the breakage ofthe P E Ochains by a seriesof U Vinitiated freeradicalreactions. When the free radicals induce the degradation of P E O segments in P C E,thephotodegradation of P C E mainly occursin P E Osegments. The biodegradation behavior in vitro and in vivo of polycaprolactone poly (ethylene oxide) block copolymers (PCE) has been reported in detail. Photodegradation test of PCE was performed by exposure to U Vlight. The mechanical properties and the inherent viscosity of PC Esamples which are subjected to The experimental results alsoindicated that the pure poly (ethylene oxide) (PEO) can not be photodegraded alone. A trial of the degradation rate of PCE was much more than than hydrolyzing Photodegradation of PC Ecopolymers was proposed: the carbonyl group in PC Lgments catalyze the breakage of the PE Ochains by a series of U Vinitiated Free Radical Reactions. When the free radicals induce the degradation of PEO segments in PCE, the photodegradation of PCE mainly in PE Osegments.