A new ent-kaurane type diterpenoid glycoside, 17-O-beta-D-glucopyranosyl-16alpha-ent-kauran-19-oic acid (1), together with 17-hydroxy-16alpha-ent-kauran-19-oic acid (2), 16alpha,17-dihydroxyl-ent-kauran-19-oic acid (3), and 16alpha-hydroxy-17-acetoxy-ent-kauran-19-oic acid (4) were isolated from the aerial parts of Inula japonica Thunb. The structure of 1 was determined mainly by use of 1D and 2D NMR spectroscopic techniques including HSQC, (1)H-(1)H COSY, HMBC, and NOESY. In addition, 4 exhibited significant inhibitory activity on NO production in LPS-stimulated RAW264.7 cells with IC(50) value of 14.3 microg/mL.