Polyethyleneimine(PEI)-coated ZnSe quantum dots dispersed in water were fabricated by femtosecond laser ablation in fluid.The dispersion liquid exhibites an appearance of bright yellowish transparent liquid.A few quantum dots aggregated in water and formed spherical micelles.From the scanning electron microscope(SEM) test,the micelles have an average diameter about 40~100 nm.High resolution transmission electron microscopy(HRTEM) and X-ray diffraction(XRD) were used to study the crystallographic characteristics of ZnSe.Test results show that the quantum dots remained the Zinc blende crystal structure of the bulk materials.This PEI-coated ZnSe quantum dots dispersion liquid shows bright green fluorescence under irradiation of 365 nm UV light.The fluorescence center wavelength is about at 500 nm.Photoluminescence spectra and UV-Vis absorption spectra were used to study the pH response property of the PEI-coated ZnSe quantum dots.Results indicate that with the decrease of pH value from 9 to 4,the photoluminescence spectra peak show a blue shift to a short band and the maximum value of the blue shift is 25 nm.A possible mechanism for the origin and the tunability of the green fluorescence was discussed.