CeO2/TiO2composite nanoparticles with different Ce/Ti molar ratios have been successfully synthesized via sol–gel method. It was found that the band gap of the nanocomposite is tunable by varying Ce/Ti content. The nonlinear response of the sample was studied by using the nanosecond laser pulses from a Q switched Nd:Yag laser employing the Z-scan method. Open aperture Z-scan experiment revealed that with the increase in the CeO2amount in the nanocomposite, the non-linearity of the composite increases, and it was assumed that this could be due to the modification of TiO2dipole symmetry by the addition of CeO2. Closed aperture Z-scan experiment showed that when the CeO2amount increases,positive nonlinear refraction decreases, and this could be attributed to the increase in the two photon absorption which subsequently suppresses the nonlinear refraction. Ce was found that the band gap of the nanocomposite is tunable by varying Ce / Ti content. The nonlinear response of the sample was studied by using the nanosecond laser pulses from a Q switched Nd: Yag laser employing the Z-scan method. Open aperture Z-scan experiment revealed with the increase in the CeO2amount in the nanocomposite, the non-linearity of the composite increases, and it was was was was assumed Closed aperture Z-scan experiment showed that when the CeO2amount increases, positive nonlinear refraction decreases, and this could be attributed to the increase in the two photon absorption next suppresses the nonlinear refraction.