The formation, development, extinction of vocabulary is somewhat related to a social phenomenon. Especially the recent rapid progress of Internet environment is making many changes of people s communication. People think the anonymity is important because of the easiness, quickness and concealment. this tendency made temporary fad words and slangs on the Internet. Dealing with the formation of neologisms on the Internet has the following meanings. First, neologisms belong to present Korean vocabularies in use. Second, there are two points of view on neologisms. One is a positive view of proliferation, another is a negative view of destruction.This study deals with the meaning characteristic, categorization, transparency and acceptability of typical neologisms. In Chapter 2, the meaning characteristic and three ways of formation of neologisms are discussed. In Chapter 3, focused on the ordinary fad words and slangs among neologisms, neologisms are categorized according to the meaning characteristic which has phonological characteristic, morphologic characteristic, semantic characteristic. In Chapter 4, the transparency and acceptability of neologisms are discussed. the transparency is categorized into opaqueness, translucency and transparency, the factors of acceptability are the word formation, native words, the currency, the popularity and so on.