The viscoelastic properties of a series of syndiotactic polystyrene (s-PS) melts with high stereoregularity and different molecular weights (M(w) = 134-1160 kg/mol) are measured in a wide achievable temperature range (270-310 degrees C) to determine the entanglement molecular weight (M(e)) and flow activation energy (E(a)). In addition, four actactic polystyrenes (a-PS, M(w) = 215-682 kg/mol) and one isotactic polystyrene (i-PS, M(w) = 247 kg/mol) are also studied to elucidate the tacticity effect on the corresponding properties. Using a reference temperature of 280 degrees C, the master curves of dynamic storage and loss modulus are constructed according to the time temperature superposition principle. On the basis of the classic integration method, the M, values are determined to be 14 500 and 17 900 g/mol for the s-PS and a-PS, respectively, which are significantly lower than that for the i-PS, similar to 27 200 g/mol, derived from the Wu's empirical equation. Owing to the difference in M(e) at a fixed M(w) the viscosity of i-PS is about 1 order of magnitude lower than that of s-PS and a-PS. However, when double-logarithmic plotting of the melt viscosity against the M(w)/M(e) is performed, a self-consistent behavior is seen for all the PS used despite of the differences in the M(w) and chain tacticity; the derived exponent is 3.61. According to the Arrhenius plot, the determined E(a) for the s-PS is 53 +/- 5 kJ/mol, which is apparently lower than that for the other two isomers possessing a similar value of 90-107 kJ/mol.