The architecture of participation and sharing that encourage users to add value is one of the fundamental characteristics of a successful Web 2.0 application. Blog, as a personal publish platform on the web, removes the intermediation for channel selection thus everyone can represent himself/herself without any filtering mechanism. In this research, we present a methodology to derive user's degree of expertise from blog data and conduct an experiment using data collected from a enterprise blog system. The result shows that the average precision reaches around 0.8 and which factor is useful in our proposed method.