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