The structural characteristics of flavonoids (1-3 and 6-8) from the root of Cudrania tricuspidata required for neuraminidase inhibition were studied and compared with commercially available flavonoids (4, 5, and 9-12). Alkylated flavanones (1-3) display better inhibition than the corresponding parent compound 4. Importantly, flavanone 1 bearing a C-8 hydrated prenyl group showed extremely high inhibition with IC(50) of 380 nM. On the other hand, the parent flavone 5 was more effective than alkylated analogues (6-8). Isolated inhibitors (1-3 and 6-8) showed noncompetitive inhibition in kinetic studies. The binding affinity of flavanones (1-4) for neuraminidase in in silico docking experiments correlated well with their IC(50) values and noncompetitive inhibition mode.