The sol-gel transition process of PMMA/SiO_2 hybrid materials was first studied by means of the dynamic torsional vibration method. The different stages of the transition can be described by the change of torque. The temperature-dependent measurement of the gel time(t_g) gives the possibility to determine the apparent activation energy(E_a) of this transition according to Flory′s gelation theory. The non-equilibrium thermodynamic fluctuation theory was used to predict the transition behavior. The isothermal transition experiments on hybrid sols with different TEOS(tetraethyl orthosilicate) contents were carried out. The results show that the E_a of a hybrid sol is higher than that of a non- hybrid sol of a TEOS-water-ethanol system. The increasing of TEOS content in a hybrid sol has no obvious effect on the E_a value, but it can enhance the sol-gel reaction rate. The sol-gel transition process of PMMA / SiO 2 hybrid materials was first studied by means of the dynamic torsional vibration method. The different stages of the transition can be described by the change of torque. The temperature-dependent measurement of the gel time (t_g The non-equilibrium thermodynamic fluctuation theory was used to predict the transition behavior. The isothermal transition experiments on hybrid sols with different TEOS (E_a) of this transition according to Flory’s gelation theory. tetraethyl orthosilicate) contents were carried out. The results show that the E_a of a hybrid sol is higher than that of a non- hybrid sol of a TEOS-water-ethanol system. The increasing of TEOS content in a hybrid sol has no obvious effect on the E_a value, but it can enhance the sol-gel reaction rate.