Resonantly enhanced nonlinear refraction in rare earth doped solids is studied with femtosecond degenerate pump probe two beam coupling spectroscopy. An ultrafast resonant nonlinear refractive index of the order of 1×10 -14 cm 2/W is measured in Nd∶glass, and it is 10 2 times greater than the host material. It shows that both the transient probe transmission and the nonlinear refraction can be effectively controlled via the coherent coupling of probe beam with the pump through Nd∶glass sample. The experimental observation of the femtosecond resonant nonlinear refraction response in the rare earth solids may implicate important applications in ultrafast optical switching. It shows that coherent control can be applied to improve the modulation depth of ultrafast optical switching. Resonant nonlinear refraction measurements in other rare earth doped materials such as Er∶YAG and Nd∶YVO 4 demonstrate the general applicability of the pump-probe technique.