An object of the present invention is to provide a compound that can be used as a more superior therapeutic agent for central nervous system diseases. The present invention provides a dihydrate of 7-[4-(4-benzo[b] thiophen-4-yl-piperazin-1-yl)butoxy]-1H-quinolin-2-one or of a salt thereof, and a process for producing the same.本發明之目的係提供一種可用於中樞神經系統疾病作為更優異治療劑之化合物。本發明提供一種7-[4-(4-苯并[b]噻吩-4-基-哌-1-基)丁氧基]-1H-喹啉-2-酮或其鹽之二水合物,以及其製造方法。