In the previous papers, we reported the isolation of thalicarpine, dehydrothalicarpine, ovigerine, hernangerine, hernandonine and desoxypodophyllotoxin from the root-bark of Hernandia ovigera L. collected in Hengchun peninsula, and alluded the presence of an unidentified compound-(G). The present communication deals with the characterization of this unknown substance. Compound-(G), isolated from the nonphenolic fraction of acidic chloroform soluble extract, was crystallized from chloroform-methanol as pale yellowish needles, mp. 219-220°C (dec.), [α]D +115° (c=0.1, CHCl3). It formed cherry-red precipitates in mineral acid. The ultra violet spectrum in ethanol showed maxima at 237(4.51), 271(4.44), 285sh(4.34) and 343nm(log ε 3.93). Based on elemental analysis (molecular formula C30H30O6N2·2H2O), infrared absorption (2815(N-CH3), 1600(phenyl), 1200, 1020(methoxy), 1660 cm-1(conjugated carbonyl)) and NMR spectrum (N-methyl, aliphatic methylene, methoxyls, aromatic protons including AB-quartet for oxoaporphine moiety), compound-(G) was suggested as oxothalicarpine, a dimeric benzyltetrahydroisoquinoline-oxoaporphine alkaloid, confirmed by comparison with authentic sample. Although oxothalicarpine was previously obtained as a minor by-product from oxidation of thalicarpine, our work is the first instance of its direct isolation from natural source. It is interesting to note that thalicarpine, dehydrothalicarpine, oxothalicarpine and hernandaline all co-exist in H. ovigera, which will assist in understanding the biosynthetic transformation of these compounds and the antitumor action of thalicarpine.