Isothermal crystallization and melting behaviors of poly(vinilidene fluoride) (PVDF) and isotactic poly(methyl methacrylate) (isoPMMA) blend, partially soluble blend system, were investigated by the simultaneous DSC-FTIR method. The absorption bands at 795 and 810 cm^-1, which were assigned respectively to CH₂ rocking vibration mode of PVDF in TGTG' (α-form) and T3GT3G' (γ-form) conformation, were used as an indication of each crystal form. During the isothermal crystallization, the α-form crystallized in the initial stage of crystallization, γ-form crystallized after the maximum of &alpha-form content. The transition mechanism from α-form to γ-form was estimated from the linear relationship between IR absorbance corresponding to the decrease rate of α-form and the increase rate of γ-form. The γ-form was transformed from the α-form in the solid state for the blends with PMMA content (fPMMA) lower than 0.2, and the γ-form was crystallized from the super-cooled liquid state addition with the solid state transition from the a-form for PVDF. The multiple melting peaks were observed by heating immediately after isothermal crystallization. Each melting peaks were identified as the melting of α-form, the melting of γ-form produced by the melt-recrystallization of α-form, and the melting of γ-form transformed from α-form in the solid state during the isothermal crystallization.