In order to study the effect of IFN-γ on ATP binding cassette transporter A1(ABCA1) expression and cholesterol efflux in THP-1 macrophage-derived foam cells, after exposure of the cultured THP-1 macrophage-derived foam cells to IFN-γ for different time, cholesterol efflux and ABCA1 mRNA and protein level were determined by FJ-2107P type liquid scintillator and reverse trancriptase-polymerase chain reaction(RT-PCR) and Western blot, respectively and the mean ABCA1 fluorescence intensity on THP-1 macrophage-derived foam cells was detected by flow cytometry. It was demonstrated that exposure of the cultured THP-1 macrophage-derived foam cells to IFN-γ for different time results in decreasing cholesterol efflux, the expression of ABCA1 mRNA and protein and the mean ABCA1 fluorescence intensity in THP-1 macrophage-derived foam cells in a time-dependent manner. Exposure of the cultured THP-1 macrophage-derived foam cells to IFN-γ for different time results in increasing total cholesterol, free cholesterol and cholesterol ester in THP-1 macrophage-derived foam cells in a time-dependent manner. It can be concluded that IFN-γ decreases cholesterol efflux and the expression of ABCA1 in THP-1 macrophage-derived foam cells.