The unperturbed molecular dimensions of dextran samples have been determined in dimethylsulfoxide (DMSO) solutions from intrinsic viscosity measurements at different temperatures. The unperturbed dimension parameter, K-o, has been calculated from extrapolation methods. The unperturbed root-mean-square end-to-end distance, (1/2)(o) found for the polymer samples in DMSO solutions, indicate that the polymer coils are contracted. This distance varies from 3.25 x 10(-7) cm to 2.94 x 10(-7) cm for the sample T 40 and from 8.28 x 10(-7) cm to 7.48 x 10(-7) cm for the sample T 500, in the chosen solvent as the temperature is raised from 25 degrees C to 45 degrees C. In the system of dextran/DMSO, the long range interaction parameter, B, was also determined and a significant decrease is observed between 25 degrees-45 degrees C. The theta temperatures, Theta, were obtained as Theta = 327.25 K, Theta = 327.41 K and Theta = 323.38 K from the temperature dependence of the interaction parameter in Kurata-Stockmayer-Fixman, Berry and Inagaki-Suzuki-Kurata equations, respectively.