Abstract: OBJECTIVE To explore the effect and possible mechanism of the extract of barks of Michelia macclurei Dandy.(EBMMD) on apoptosis-inducing in HepG2 cell lines in vitro. METHODS The effect of apoptosis-inducing of EBMMD on HepG2 cell lines and expression of COX-2 protein were explored by inverted microscope and flow cytometry assay as well as Western-blotting assay. RESULTS The apoptosis-inducing of EBMMD on HepG2 cells was observed in concerntration-dependent manner by flow cytometry, and the cell morphology change was observed by inverted microscope. EBMMD showed growing inhibitory effects on the expressions of COX-2 protein in concerntration-dependent manner and significant inhibitory effect on the expression of COX-2 protein at a high concentration(25.00 μg·mL^-1) . CONCLUSION EBMMD can significantly induce HepG2 cells apoptosis, the possible mechanism may relate to downregulate the expression of COX-2 protein to induce apoptosis.