We investigated the inhibitory effect of Magnolia obovata Thunb. bark ethanol extracts on human fibrosarcoma HT-1080 cells invasion in a reconstituted basement membrane [Matrigel (MG)]. We found that the effective components of the bark ethanol extracts were magnolol and honokiol, two biphenyl compounds. The extracts, magnolol and honokiol, did not affect HT-1080 cells adhesion to MG, but did inhibit HT-1080 cells migration at a high concentration (100 microM). HT-1080 cells secrete matrix metalloproteinase (MMP)-9, which degrades the extracellular matrix as a part of the invasive process. Magnolol and honokiol inhibited the activity of MMP-9, which may have been responsible, in part, for the inhibition of tumor cell invasiveness.