Chemical constituents of Inula japonica were isolated and purified by repeated column chromatographies, over silica gel, and Toyopearl HW-40, and preparative HPLC. On the basis of spectral data analysis, including NMR and MS data, the structures of the isolates were elucidated and their anti-inflammatory activities were assayed. Fifteen compounds were isolated from the ethyl acetate extract of I. japonica, and their structures were elucidated as dihydrosyringenin (1), (3S, 5R, 6S, 7E)-5,6-epoxy-3-hydroxy-7-megastigmen-9-one (2), (6R, 7E) -9-hydroxy-4,7-megastigmadien-3-one (3), arnidiol (4), taraxasterol acetate (5), 8,9,10-trihydroxythymol (6), taxifolin (7), luteolin (8), napetin (9), eupatin (10), spinacetin (11), quercetin (12), p-hydroxycinnamic acid (13), caffeic acid (14), and caffeoyl acetate (15). Compounds 1, 2, 7, 13 and 15 were isolated from the genus Inula for the first time, and compounds 3, 4, 9-11 and 14 were isolated from this plant for the first time. The anti-inflammatory activity result showed that compounds 3, 6-12 and 14 exhibited inhibition effect against leukotriene C4 (LTC4) synthesis and degranulation definitely in c-Kit Ligand (KL) induced mast cells, and compound 8 and 12 also had the suppression effect against lipopolysacharide(LPS) induced nitric oxide (NO) activity in RAW264.7 macrophages. It is firstly reported that compounds 7 and 9-11 possessed potent inhibition activities against LTC4 generation and degranulation in mast cells.