In crystalline polymer/amorphous polymer blends the crystalline component crystallizes out, however low its concentration in the blend, if the blends are left at room temperature for months/years after its preparation, provided the diffusion is permissible at room temperature. This phenomenon has been termed ’kinetic immiscibility’ in crystalline polymer/amorphous polymer blend. Blends of poly(vinylidene fluoride) (PVF2) samples with poly(methyl acrylate) (PMA) and poly(vinyl acetate) (PVAc) have been studied with varying concentration, molecular weight and H-H defect of PVF2. The crystallization rate of PVF2 in the blends was measured by d.s.c. in the endothermic way and has been explained by the modified Lauritzen-Hoffman (L-H) growth rate theory applicable to the blends. The results suggest that the nucleation term, transport term and the concentration of crystallizing unit are the governing factors for the kinetic immiscibility. The molecular weight of the crystalline polymer has a significant effect on its crystallization in the blend because it directly effects the diffusion processes retarding the depletion of amorphous polymer from the crystalline growth front. This study places a warning on the use of transparent homogeneous crystalline polymer/amorphous polymer blends.