A phenolic compound responsible for anti-MMP-9, which is known to be involved in tumor cell invasion and metastasis, has been isolated from methanol extracts prepared from stem barks of Euonymus alatus by assay-guided fractionation. The compound has been identified as 5-caffeoylquinic acid (chlorogenic acid; CHA) by NMR and FAB-MS. CHA showed a strong inhibitory effect of matrix metalloproteinase (MMP)-9 activity in a concentration-dependent manner on zymography. The purified CHA inhibited MMP-9 activity with the IC50 of 30-50 nM. Furthermore, the cytotoxic survival curve showed that CHA does not have cytotoxic effects on cellular proliferation, when Hep3B cells were treated with various concentrations of CHA and cell viability was measured using the XTT assay. The present data suggest a clue for possible mechanisms of cancer chemoprevention by CHA and other naturally occurring phenolic compounds. The results also imply that useful cancer chemopreventive agents can be further identified by combinations of in vitro (as a first screen) and in vivo studies.