Two new biphenyl ether lignans, named obovatol and obovatal, were isolated from the leaves of M. abovata Thunb. (Magnoliaceae), and their chemical structures were determined to be 4'',5''-diallyl-2,3-dihydroxybiphenyl ether and 3,4-dihydroxy-5-(p-allylphenoxy)cinnamic aldehyde, respectively, by means of chemical and spectral studies. The former substance showed antibacterial activity against a cariogenic bacterium, Streptococcus mutans, but was less active than magnolol and honokiol.