The dynamic light scattering measurements were performed for moderately concentrated entangled solutions of atactic polystyrene in benzene (BZ) at 25.0 degreesC, in cyclohexane (CH) at 34.5 degreesC (Theta), and in diethyl malonate (DEM) at 35.0 degreesC (Theta) to characterize their viscoelastic properties. The results have shown that while the mutual diffusion coefficient D increases in the BZ solutions and decreases in the CH and DEM solutions with increasing polymer mass concentration c, the friction coefficient zeta for the three solutions increases with c showing the same power-law behavior irrespective of the weight-average molecular weight M-w and solvent quality. It has been found that the instantaneous longitudinal modulus L-0 for the CH and DEM solutions increases in proportion to c(2), obeying the familiar relation for the plateau value (4/3)G(N) of the longitudinal stress relaxation modulus, but the L-0 values for these solutions are somewhat smaller than the values predicted from the relation. The terminal relaxation time tau(m) for the two Theta solvent systems has been found to follow the power-law tau(m) proportional to c(2.7), showing good correspondence to the relation established by theological measurements.