Many existing knowledge management systems have been employing blogging services which is capable of providing various services to people. However, content delivering service among bloggers is not taking into account context (or semantics) of the contents, so that the service can spread irrelevant information into blogs. In order to solve this problem, this study proposes a blog context overlay network architecture for context matching between blogs. It is referred to as detecting “shared” context Thus, we can identify a community of practice (CoP) on blogosphere, with respect to contexts. As a result, newly generated knowledge can be proactively diffused to the blogs of which context is relevant to the knowledge, before the bloggers’ queries are asked.