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. Items are explained in Japanese. The articles can be accessed by anybody without any fee. The dictionary is managed by the Editorial Committee headed by Drs. Keiji Tanaka and Katsuhiko Mikoshiba (both in RIKEN Brain Science Institute) as a part of the Japan Node of International Neuroinformatics Coordination Facility. Our effort is totally non-profit, researcher-initiated, public awareness activity.