Dynamic mechanical properties of the partially cured unsaturated polyester were measured as a function of temperature, gel fraction and degree of cure (α) by using the Rheometrics Dynamic Spectrometer. As the degree of cure increases, the dynamic storage modulus G'' increases nearly linearly and the slope changes at the gel-glass phase transition point. However the dynamic loss modulus G" versus temperature shows a peak associated with glass transition. The T_g measured from peak temperature increases with degree of cure and the relationship between 1/T_g and α yields a good linearity. This result suggests that the curing reaction is kinetically controlled even at higher conversions.