We report on large two-photon absorption(TPA)in ZnO/ZnS and ZnO/ZnS/Ag core/shellquantum dots(QDs),determined by both Z-scan and pump-probe techniques with femtosecond laserpulses.The intrinsic TPA coefficients of ZnO-based core/shell QDs are enhanced with nearly threeorders of magnitude compared to that of ZnO bulk counterpart,which is attributable to quantumconfinement effect.The TPA cross-section of ZnO-based nanocomposites is determined to be~4.3 ×10–44 cm4 s photon–1 at the wavelength of 660 nm.This value is at least two orders of magnitudegreater than that of ZnS,ZnSe,and CdS QDs.Due to the local field effect,the nonlinear absorption inZnO/ZnS core/shell QDs is improved as beaded with Ag nano-dots.