U sing both INDO/SCI and INDO/SDCI methods, the UV-visibie spectra of C60 have been calculated. The results are in good agreement with experiment, On the basis of cnorrect electronic spectra, calculations of Ihc nonlinear third-order optical suscepti-bility (yijkl) of C60 are reported. The calculations are performed using the INDO/CI melhod combined with a sum-ver-tates expression for yijkl. The calculated resulls, <y>(-ω, ω, -ω, ω)=730×10-34 esu (ω=1.064μm) and <y>(-2ω; ω, ω, 0)=6.90×10 -34 esu (ω=1.91μm), are in good agreement with some of the reeent obserations too.