Objective:To develop and optimize a novel assay for determination of cytotoxicity based Calcein -AM release.Methods:The target cells stained by Calcein-AM dye,then effectors and targets were incubated at E/T ratios from 30∶1-1∶1 for 4 h at 37℃,and the supernatant of reactions were detected by Fluorescence-Measurement to analyze specific cytotoxity.Results:The optimal excitation and emission wave lengths of Calcein were 485 nm and 515 nm.Dilutions of target cells stained by Calcein-AM had a linear relationship with measured fluorescence values.The Calcein-AM dye used to stain the living cells was shown to have a low spontaneous leakage rate-less than 15% in 4 hours at 37℃.Cytotoxicity activity of CIK showed a significant and positive correlation with E/T ratio when incubated at 4 h.Conclusion:The developed cytotoxicity test by Calcein-AM release is accurate and can avoid the application of radioactive reagents.