Abstract: Blog has been a very important medium for some overseas Chinese in English speaking countries In reading their blogs, it is easy to notice a large amount of codeswitching phenomena In this thesis, the author draws examples from blogs written by overseas Chinese, in order to elicit the classification of situations in which the codeswitching phenomena come forth For most of the articles in blogs, Chinese as the mother tongue is used as the basic language Also, the author analyzes the cause of codeswitching in blog writings Two major factors have resulted in it One is the internal causes and the other is the external influence The two factors can be further analyzed into several other causes Internal causes include bloggers’consideration of habituation, theory of economy, needs for conciseness and the superiority of language External influence includes the influence of speech communities, the social identity and the social and economic development in China

Key words: codeswitching, blog, overseasChinese