A new C‐glycosyl flavone containing a 3‐keto sugar, isocassiaoccidentalin B (1), was isolated from whole Cassia nomame (Sieber) Honda plants, along with eleven known compounds, including two flavonoids (2 and 3), five flavonoid glycosides (4 – 8), two chalcones (9 and 10), and two phenylpropanoids (11 and 12). The chemical structures of all compounds were determined via 1D‐ and 2D‐NMR, and ESI‐MS. Among these, compounds 2, 3, 7, and 8 were found to be the most potent in inhibiting nitric oxide release. Compounds 1, 2, 4, 8, 9, and 10 showed significant free‐radical scavenging activity.