A fructan, Opaw-2, with molecular mass of about 14 kDa, was isolated from the tuberous roots of Ophiopogon japonicus. Opaw-2 comprises fructose and glucose with a molar ratio of 30:1. Linkage and NMR analyses indicated that Opaw-2 has a backbone structure of beta-(1-->2)-Fruf and beta-(2-->6)-Fruf residues that branches at O-6 of beta-(1-->2)-Fruf residues with alpha-1-linkage to the Glcp residues and terminates with Fruf residues. In cultured lymphocytes, the application of Opaw-2 significantly stimulated the proliferation of lymphocytes in a dose-dependent manner. By using atomic force microscopy, Opaw-2 showed a morphological change from globular to helical fibrous shape at increasing concentrations.