Poly(d,l-lactide-co-p-dioxanone) (P(LA-co-PDO)) copolymers with different chain microstructures were synthesized by one-step or two-step bulk ring-opening polymerizations of d,l-lactide (LA) and p-dioxanone (PDO) monomers using stannous octoate [Sn(Oct)_2]/n-dodecanol as the initiating system. The average sequence lengths of the lactidyl (LL^) and dioxanyl (L_(PDO)) units were calculated from the ~1H NMR spectra. It was found that both L_(LA) and LpDo values from the two-step syntheses were significantly longer than those from the corresponding one-step syntheses, indicating more blocky structure achieved for the two-step copolymers. Corresponding to this difference in microstructure, the two-step copolymers were semi-crystalline, while the one-step copolymers were completely amorphous. In conclusion, the crystallinity of P(LA-co-PDO) copolymers could be adjusted conveniently to meet specific applications by changing the microstructure of the eopolymers via different polymerization routes.