Poly(epsilon-caprolactone)-poly(L-lactide) (PCL-PLLA) block copolymers were synthesized via melt or solution sequential copolymerization of epsilon-caprolactone (epsilon-CL) and L-lactide (L-LA) using nontoxic dibutylmagnesium as initiator. The formation of block structure was confirmed by H-1-, C-13 NMR, GPC, and FT-IR, it can be concluded that the block copolymers PCL-PLLA have been successfully synthesized by both melt and solution sequential copolymerization methods. Two melting endothermic peaks (T-m) during heating and two crystallization exothermal peaks (T-c) during cooling were observed in DSC curves. XRD patterns of the copolymers were approximately the superposition of both the PCL and PLLA homopolymers. The results indicated the coexistence of both PCL and PLLA crystalline microdomains, and the microphase separation took place in the block copolymers.