We report the measurements of the nonlinear refractive index of porous silicon photonic crystal by the reflection Z-scan t echnique at 1064nm.The measured nonlinear refractive indices of porous sili- con microcavities of n₂=－(2.16±0.15)×10－10 cm²·W－1,poro us silicon Bragg mirrors of n₂=－(7.24±0.17)×10－10 cm²·W－1 and porous silicon polybasic multilayer of n₂=－(3.73±0.09) ×10－9cm²·W－1 are obtained from the curves.The negativ e value at the photon energy even well below the bandgap suggests that the optic al Stark effect gives the most contribution to the optical nonlinearity of the nanostructures.T he experimental results indicate an enhancement of the nonlinear refractive index of porous si licon polybasic multilayer,which suggests one-dimensional porous silicon photonic crystals for nonlinear optical applications,such as power limiting and optical switching.