The activation energy ΔEa for diffusion of water molecules into untreated thin film of poly(vinyl alcohol) (PVAVTFA) derived from vinyl trifluoroacetate was estimated as 30.3 kcal/mol from the temperature dependence of the initiation time of swelling. The degree of equilibrium swelling increases with the increase in temperature in the range of 10–70°C, passing through the constant range between 30 and 50°C. Under the forced, repeated elongation and contraction for swollen PVAVTFA thin film in water, the perfect elastic behavior is kept up to higher elongation with the increase in temperature and especially up to about three times equilibrium swelling length at 70°C. Young's modulus of swollen PVAVTFA thin film in water was 6.47 × 106 to 1.60 × 106 dyn/cm2 at 25–70°C. The molecular weight between junctions Mc increased with the increase in temperature; Mc was nearly equal to about one-sixth of the molecular weight of raw polymer M at 25°C and about one-third of M at 70°C. The interaction parameter between PVAVTFA and water X1, was 0.493–0.497 at 25–70°C.