This paper suggests the education method of information communication ethics by harmful word filtering on web boards as a way to solve the malfunctioning problem occurring in making informations at the step of their positive activities of information offers. The harmful word filtering system for the education of information communication ethics describes the method to construct a harmful word dictionary by extracting harmful words related with improper doing of writing, sexual insult, abusive language and expressions of criticizing others shown in web boards. Decrease by more than 90% in writing with harmful words and inappropriate writing was shown as the result of application of the harmful word filtering system on school home pages.