The optical nonlinearity induced by electrical poling decays gradually in poled polymers. This suggests that the molecular alignment can be reoriented in the polymer matrix at room temperature by the external electric field. We measured the frequency responses and the temperature characteristics of second‐harmonic generation (SHG) in a dye doped polymer in order to clarify the electric field dependence of the nonlinearity. The experimental results show that there is a slow response of the SHG coefficient variation due to the reorientation of nonlinear molecules and another fast response. This characteristic can be applied to develop a new type of nonlinear optical devices by dynamically controlling the nonlinearity of the material by the external electric field. ©1996 American Institute of Physics.