The compatibility of a poly(vinylidene fluoride)/poly(methyl methacrylate) (PVDF/PMMA) blend and the crystal structure of PVDF were examined according to the blend ratio, the cooling speed from the melt state, and the annealing condition. Different crystal structures, PVDF (form I) and PVDF (form II), could be produced from the PVDF/PMMA blend. Generally, the crystal structure of PVDF (form I) is difficult to obtain. By melting PVDF/PMMA (70/30 to 80/20 wt %) blends, quenching, and annealing at 120 degrees C, we found that the crystal growth of PVDF (form I) was predominant. The crystallization speed of PVDF seemed to depend upon the compatibility of the PVDF/PMMA blend. PVDF crystallized slowly when the compatibility of the blend was high, resulting in the formation of PVDF (form I). (c) 2005 The Electrochemical Society.