The value of dln[n]θ／dlnT for a polydimethylsiloxane fraction of Mn=1．4×106 has been determined in a temperature range of 10一100℃ by using a series of θ-solvents made of ethylbenzene-diethylphthalate．The compositions of these θ-solvents at various temperatures were determined by the precipitation threshold method of Elias，and finally confirmed by light scattering to give vanishing second virial coefficient．The results show that dln [n]θ／dlnT=0.45．Using the Flory-Fox theory of intrinsic viscosity we get din h20／dlnT=0.30，that is，the unperturbed dimension of polydimethylsiloxane mole-cult increases with increasing temperature．This seems reasonable in view of the dipole-dipole interactions of the Me2SiO units along the chain，so that the gauche conforma-tion has lower energy than the trams conformation．