This Article aims to discuss whether P2P website operator's providing peer-to-peer file-sharing service constitutes the aiding in the commission of unauthorized reproduction or distribution offense. The term ”neutral business activity” refers to the business activity which is conducted relying exclusively on its own purposes without any reference to the behavior of the traders or trading circumstances. Many German commentators have argued that business activity may not be imposed aiding liability without taking its neutral nature into account. The ezPeer court decision also adopted similar opinion. This Article first provides a study of many aspects of the neutral business activity doctrine in the German criminal law. Next the Author discusses the applications of this doctrine to P2P website operator's liability.