Thermochromic polymer nanocomposite films were prepared from polymerizable organogels. Organogelator 1 had a structure which 3,4,5-tris(ω-decenyl)benzamide groups were attached to a quarterthiophene core through amide bonds. Organogelator 2 had the same structure except that tris(ω-decenyl) groups were replaced by tris(n-decanyl) groups. The PMMA nanocomposite films were prepared by the photopolymerization of the organogels formed in methyl methacrylate (MMA). The film containing 1 (0.5 wt%) showed reversible thermochromism. The emission under 365 nm irradiation was changed to bright green from orange by heating up to 120 °C and returned to its initial orange by cooling. To the contrary, the PMMA composite film prepared from the organogel of 2 (0.5 wt%) did not show a reversible thermochromic property. Organogelator 1 with polymerizable terminal vinyl groups was covalently embedded in the PMMA matrix, but 2 was not. The reversible thermochromism was likely caused by the thermally reversible conformational change of quarterthiophene units in the polymer fibers.