Objective To study the chemical constituents from Onychium japonicum.Methods Che-mical constituents were isolated by repeated column chromatography and preparative HPLC,and their structures were elucidated on the basis of spectroscopic method.Results Ten compounds were identifed as:4,3',4'-trihydroxy-2,6-dimethoxychalcone(1),chrysoeriol(2),luteolin(3),butin(4),protocatechuic acid(5),3,4-dihydroxy-acetophenone(6),caffeic acid(7),vanillic acid(8),2,4-dihydroxybenzaldehyde(9),syringic acid(10),and ?-sitosterol(11).Conclusion Compound 1 is a new product named japonicone D,compounds 2-10 are isolated from the plants of Onychium Kaulf for the first time.