The rheological properties of poly(trimethylene naphthalene-2,6-dicarboxylate) (PTN) were studied using a dynamic stress rheometer with oscillatory parallel plates. The influence of temperature and molecular weight on the storage modulus, loss modulus, and complex viscosity was investigated. It was possible to express the temperature dependence of the shift factors a(T) with the Arrhenius equation; the activation energy was found to be 85 kJ/mol. A comparison of molecular weight determined: (a) by rheological measurements and (b) by Mark-Houwink-Sakurada equation showed excellent agreement.