In this study, CdSe/CdTe Type-II quantum dots (QDs) were synthesized using dropwise method. The core/shell nanocrystals have been characterized by UV–Vis absorption and photoluminescence (PL) spectroscopies, transmission electron microscopy and z-scan technique. Nonlinear properties of each type of quantum dots were studied using femtosecond(fs) z-scan method at 800 nm wavelength with different laser intensities. Fs laser z-scan experimental set-up are used to determine two photon absorption coefficient (β ̴10−12 cm/W) and nonlinear optical Kerr coefficient (n2 ̴ 10−20 cm2/W. The imaginary and real parts of third order susceptibility (X(3)) were calculated based on β and n2 under different laser intensities for seven different core/shell QDs. Third order susceptibility for CdSe/CdTe type II QDs was found to be about 10−12 esu.