In this study, the effects of temperature on dielectric parameters of MOS capacitor with thermal oxide layer have been investigated using admittance spectroscopy technique. The dielectric parameters such as dielectric constant (epsilon'), loss (epsilon ''), loss tangent (tan delta) and ac conductivity (sigma(ac)) were calculated from capacitance (C-m) and conductance (G(m)) measurements. The Cm and Gm measurements were carried out in a wide range of temperatures (100-400 K) at 1 MHz. The increase of C-m and G(m) with the increasing temperature can be attributed to the interfacial space charge formation and increment in thermal activation of charges. The value of epsilon', epsilon '' and ac conductivity increases with the increase in temperature. Also, the activation energy calculated from the temperature dependence of ac conductivity was found to be about 21 meV.