We describe the luminescence spectral properties of CdS nanoparticles with multiphoton excitation. Three types of CdS nanoparticles were examined which were a CdS/dendrimer composite which displays high anisotropy, Cd2+-enriched nanoparticles which display two emission maxima, and polyphosphate-stabilized nanoparticles which display long wavelength emission. Illumination with long wavelengths near 700-790 nm resulted in two-photon excitation. Essentially the same emission spectra and intensity decays were observed with one-photon and two-photon excitation. Comparison with fluorescein indicates the NPs display large two-photon cross sections near 100 GM. The CdS/dendrimer and Cd2+-enriched CdS nanoparticles displayed large anisotropy values with two-photon excitation, substantially larger than with one-photon excitation. It appears that semiconductor nanoparticles are comparable to organic fluorophores which display the same spectral properties with one-photon and two-photon excitation.