A new ent-kaurane type diterpenoid glycoside, 17-O-$eta$-D-glucopyranosyl-$16{alpha}$-ent-kauran-19-oic acid (1), together with 17-hydroxy-$16{alpha}$-ent-kauran-19-oic acid (2), $16{alpha}$,17-dihydroxyl-ent-kauran- 19-oic acid (3), and $16{alpha}$-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, $^1H-^1H$ 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 $14.3;{mu}g/mL$.