Abstract: OBJECTIVE To investigate the chemical constituents from the whole plant of Lycopodium japonicum. METHODS The whole plant of L. japonicum was refluxed with 80% ethanol. The concentrated extract was dissolved in 1% HCl solution. The supernatant was then basified and partitioned with EtOAc. The EtOAc fraction was chromatographed on silica gel column, purified by MPLC and preparative HPLC. The structures of isolated compounds were elucidated on the basis of spectroscopic data analyses. RESULTS Eleven compounds were isolated from the ethanolic extract of L. japonicum, including eight alkaloids:α-isoobscurine (1), α-obscurine (2), des-N-methyl-α-obscurine (3), lycodoline (4), lycoposerramine M (5), obscurinine (6), lyconadin D (7), and lycoflexine (8); two triterpenoids:lycoclavanol (9), α-onocerin (10); and a phenolic glycoside:4-glucosyloxy-3-methoxyphenyl trans-propenoic ethyl ester (11). CONCLUSION Compound 1 is a new compound and named α-isoobscurine. Compounds 7 and 11 were isolated from this plant for the first time.