Accelerated crystallization of poly(L-lactide) (PLLA) homo-crystallites occurred in the presence of poly(L-2-hydroxybutyrate) [P(L-2HB)], poly(D-2-hydroxybutyrate) [P(D-2HB)], and the mixture of P(L-2HB) and P(D-2HB) [P(L-2HB)/P(D-2HB)]. The accelerating effect of incorporated polymers decreased in the following order: P(L-2HB)/P(D-2HB) > P(D-2HB) > P(L-2HB) > none, for heating and isothermal crystallization for T-c of 130 and 135 degrees C and P(D-2HB) > P(L-2HB)/P(D-2HB) > none > P(L-2HB), for cooling. The P(L-2HB)/P(D-2HB) homo-stereocomplex (HMSC) crystallites, P(D-2HB)/PLLA hetero-stereocomplex (HTSC) crystallites, and P(L-2HB) or P(D-2HB) homo-crystallites are found to be promising biodegradable nucleating agents for PLLA homo-crystallization. The P(L-2HB)/P(D-2HB) HMSC crystallites are most effective during isothermal crystallization and nonisothermal crystallization with heating, whereas the P(D-2HB)/PLLA HTSC crystallites are most effective during nonisothermal crystallization with cooling from the melt. In addition to the nucleating effect, the plasticizing effect of free P(2HB) chains increases both G and the PLLA spherulite number per unit mass. These effects result in accelerated crystallization of PLLA homo-crystallites. (c) 2011 Wiley Periodicals, Inc. J Appl Polym Sci 122: 321-333, 2011