The Patent Reexamination and Invalidation Department (PRID) of the China National Intellectual Property Administration (CNIPA) maintained the validity of CN Invention Patent No. ZL02123000.5 (the ’000 patent) in an invalidation proceeding. The PRID held that the claimed invention is inventive because: (1) one person of ordinary skill in the art would not have been motivated to increase the water-solubility of butylphthalide by complexation with hydroxypropyl-β-cyclodextrin; and (2) one person of ordinary skill in the art would not have expected that the increase of the water-solubility would be sufficient to allow a therapeutically effective amount of butylphthalide to be delivered in aqueous formulations. The PRID appeared to adopt the “reasonable expectation of success” requirement in the U.S. patent practice. Although prior art references establish that cyclodextrin derivatives can improve water solubilities of compounds having low or no water solubilities, the claimed invention is not obvious because one person of ordinary skill in the art would not have had reasonable expectation that the increase of the water-solubility of the complex of butylphthalide with hydroxypropyl-β-cyclodextrin allows the therapeutic use of butylphthalide in aqueous formulations.