Abstract: Influence of heating or annealing at different temperatures from 25 to 140 °C on the uniaxial tensile properties of polyvinyl alcohol (PVA) thin films was investigated by using tensile testing method. It was observed that especially the shape of initial part (up to 10% strain) of the stress-strain curve changed significantly which indicates the formation of a transition point at a low strain value of around 1-2% strain with increasing anneal temperature. Besides, initial or Young’s modulus increased from 0.26 GPa to around 1 GPa as the temperature increased from 25 °C to around 100 °C and then it decreased slightly down to around 0.7 GPa. Ultimate tensile stress increased significantly from around 16 to 39 MPa. Moreover, toughness of the PVA films were improved from around 144*104 to 3942*104 J/m3 for the anneal temperatures from 80 to 130 °C. By using the FT-IR/ATR spectral results, the increase in tensile strength and toughness is assumed to be due to increase in the degree of crystallization and absorbance ratio of hydrogen bonded OH groups, that is, the increase in the more ordered structural units and reformation and/or breakage of intra- and inter-molecular hydrogen bonds during heating process.