The Flory-Huggins interaction parameter (chi(12)) between poly(vinylidene fluoride) (PVdF) and organic solvent was estimated experimentally over wide range of temperature by an inverse gas chromatography (IGC) using many kinds of solvents such as alkane, alkene, ketone, lactone, and nitrogen-containing solvent. The thermoreversible gelation of PVdF solution was discussed from the magnitude of interaction parameter chi(12) between PVdF and solvent. The parameter chi(12) was measured for a concentrated PVdF solution by the usual IGC technique. The parameter chi(12) obtained for each PVdF/solvent system increased slowly with decreasing temperature. The present systems were divided broadly into three groups according to the magnitude Of chi(12) in the vicinity of room temperature, i.e., group (a) with chi(12) >> 0.5, group (b) with chi(12) approximate to 0.5, and group (c) with chi(12) << 0.5. The group (b), to which ketone and lactone belong, converted to thermoreversible gels accompanying with crystallization of polymer. The gelation process of PVdF solution was investigated through measurement of in situ Fourier transform infrared (FT-IR) spectroscopy. The time-resolved FTIR spectra suggested that the gelation took place taking the conformation T(3)GT(3)(G) over bar for the system where the parameter chi(12) was nearly equal to 0.5 such as PVdF in gamma-butyrolactone. For the system where the parameter chi(12) became larger than 0.5 such as PVdF in cyclohexanone, 3-pentanone, 3-hexanone, 3-heptanone, or 3-octanone, the gelation occurred taking the conformation TGT (G) over bar.