Brain Science Dictionary is an online dictionary for students and researchers in neuroscience field. It is in a Wikipedia style but written only by invited authors with peer reviewing process. Articles are explained in Japanese, which can be accessed by anybody without any fee. The dictionary is managed by the Editorial Committee chaired by Dr. Yasunori Hayashi (in Kyoto University Graduate School of Medicine) as an official activity of the The Japan Neuroscience Society with support of RIKEN Center for Brain Science. Our effort is totally non-profit, researcher-initiated, public awareness activity.