A method of processing tag information includes displaying a web page for designating media contents to be uploaded on a screen of the client terminal; receiving tag information on the media contents to be uploaded through the web page; converting the received tag information into metadata; storing the metadata in a local storage area of the client terminal; and storing the metadata in a storage area of a web server. Also provided is a client-server system using the method. Accordingly, the tag information, which provides additional information associated with multimedia contents, can be managed at a local area and on a web connected to the local area through the communication network. Also, a user environment in which the tag information can be applied in a useable way at the local area is provided. The tag information is added to the multimedia contents stored in the local area, so that it is not necessary to manually input the tag information each time the contents are uploaded.