Recently much attention has been paid to polylactides, because they are biodegradable in the human body as well as in the each environments. These polymers can be synthesized by ring-opening polymerization of lactides or polymerization of lactic acids to have a variety of molecular weight and chemical composition. Physical properties of polylactides are affected by many factors including molecular alignment, microphase structure, and polymer blending as well as molecular characteristics. The change of physical properties of polylactides upon hydrolysis is also influenced by the above mentioned factors. These lactide polymers can form different crystalline structures including homo-crystallites, stereocomplex crystallites, and spherulites. Stereocomplexation (racemic crystallization) occurs between poly(L-lactide) and poly(D-lactide). This review article will demonstrate that the biodegradable materials having a wide range of physical properties can be synthesized not only by copolymerization and blending but also by altering the highly ordered structure of polylactides.