A biodegradable block copolymer has high conformability and excellent degradability. The block copolymer including a polyalkylene glycol block and a polyhydroxyalkanoic acid block, wherein the mass ratio of the polyalkylene glycol block with respect to the total mass is 10 to 60%; the carbonyl carbon has a carbon nuclear relaxation time T1ρ of not more than 20 ms; and the block copolymer satisfies Equation (1): χ=χ1×χ2>20 (1) χ1: crystallization rate of the polyalkylene glycol block; χ2: crystallization rate of a poly-A block, wherein A represents, among the repeat units contained in the polyhydroxyalkanoic acid block, a repeat unit whose homopolymer composed of the same repeat units has a highest crystallization rate.
BIODEGRADABLE BLOCK COPOLYMER