The expansion behavior of polystyrene(PS) chains with various molecular weights has been investigated above Flory Θtemperature by viscometry after dissolving in the three different mixed solvents systems such as benzene/n-heptane, 1,4-dioxane/isopropanol, and 1,4-dioxane/n-heptane. Two different regimes are observed as increasing temperature: one regime is for the expansion of chain and the other is for the contraction. For the higher molecular weight sample of PS, the higher peak temperature showing its maximum expansion is obtained. Within a certain system of PS/mixed solvents, the τ/τc parameter shows universality for the variation of molecular weight. But while each system of PS/mixed solvents has shown its own different slope, the universality breaks down in the overall system of mixed solvents. However after introducing a new empirical b2/3τ/τc parameter, all data points of three different systems have dropt on one master curve and the universality of chain expansion has recovered again. Here τ and τc are defined as (T-Θ)/Θand (Θ-Tc)/Tc, respectively and Tc is the critical solution temperature, and b of Schultz-Flory equation is corresponding to the effective slope in the plot of 1/Tc against 1/Mw1/2.