In the present study, isothermal crystallization of asymmetric PLLA/PDLA blend (4/1) at around 100 degrees C was investigated by in-situ time-resolved FTIR and Raman Imaging measurement. FTIR result indicated that crystallization of homo-crystal (HC) was retarded due to the formation of large amount of stereocomplex (SC) in the isothermal process. A unique spherulite morphology was observed through polarized optical microscopy (POM) and the distribution of SC and HC in and out of the big spherulite was revealed under the assistance of Raman imaging measurement. These results demonstrated that the SC crystal dispersed homogeneously both in the amorphous and spherulite region. However, the HC mainly located in the big spherulite area. A possible isothermal crystallization process for the asymmetric PLLA/PDLA blend was proposed.