Molar refraction (Rm), molecular radii (r), polarizability (α) and internal pressure (πi) values determined from the refractive index data for the binary liquid mixture of Tetrahydropyran (THP) with 1-hexanol have been measured at five temperatures (T=298.15, 303.15, 308.15, 313.15 and 318.15 K). The measured data utilized to evaluate the excess molar refraction (Rm E ), excess molecular radii (r E ), excess polarizability (α E ) and excess internal pressure (πi E ) along with their Redlich-Kister co-efficient and standard error values of the mixed solvents. The results show existence of weak molecular interaction in the mixture.