An all-optical switching is demonstrated by use of defect mode in two-dimensional nonlinear photonic crystals made of polystyrene. Transmittance contrast of about 70% is achieved for the probe light. The dynamical shifts of the defect mode induced by pump intensity are measured and analyzed in detail. It is found that the defect mode shifts 5 nm under the excitation of 18.7GW∕cm2 pump intensity, which is in agreement with the theoretical predictions. Time response of the optical switching is smaller than the laser pulse of about 10 ps.