The third order optical nonlinearities of SnO2 nanoparticles were studied in a nonresonant region by Z-scan technique with 18 ns, 0.53 μm pulses from a Q-switched Nd:YAG laser. The sign and magnitude of the third order nonlinear susceptibility χ(3) and two photon absorption coefficient β, et al., of SnO2 nanoparticles with different size were obtained. The experimental results were discussed in terms of the quantum confined effect.