Abstract: The two-photon absorption of water soluble CdTe quantum dots and Mn2+-doped CdTe quantum dots in four different sizes has been studied, by using the open Z-scan technique, with a Ti: sapphire laser at 800 nm wavelength, 50 fs pulsewidth, 1 kHz repetition frequency. The results show that, the two-photon absorption coefficient of CdTe: Mn quantum dots is 1.1 times that of CdTe quantum dots for the same growth time, and the relationship between the two-photon absorption coefficient of quantum dots and the particle size is inverse proportion, because the nonlinear absorption of CdTe: Mn quantum dots belongs to the saturated absorption. It is shown that Mn2+-doped quantum dots exhibit good two-photon absorption phenomenon, and have broad application prospects in optical switches and optical limiting devices.