Abstract: Prepolymer L-polylactide and D-polylactide with reactivity for condensation polymerization and different molecular weights were prepared by using lactide as monomer,lactic acid and stannous octoate as initiator and catalyst respectively.A series of stereoblock polylactides were synthesized via solid state polycondensation using precursors obtained by melting blend of L-polylactide (PLLA) and D-polylactide (PDLA) with similar weight-average molecular weights.The chain structure,molecular weight,thermal properties and crystal structure of products acquired were characterized by H-NMR,GPC,DSC and XRD,respectively.The results show that the products have stereoblock structure.The molecular weight of the prepolymers will affect the relative content of homochiral crystal and stereocomplex crystal in the precursor,and thus affect the structure of the solid-phase polycondensation product.When the average molecular weight of PLLA and PDLA are both about 5×10⁴,the molecular weight of the product increases rapidly and reaches 1.83×10⁵,and which is beneficial to the improvement of crystallinity of the stereocomplex crystal in the final product.