This research is a textual analysis aimed to study the pattern of computer-mediated communication by means of observation on internet Relay Chat (IRC). The author focused on conversations in five most popular chat rooms on two IRC networks—Assumption University’s IRC server (irc.au.ac.th) and Webmaster’s server (irc.webmaster.com). A total of three hundred texts were observed and recorded. Results of the research were as follows 1. The structure of communication consists of 3 parts: the communication from IRC servers, the communication from users and the communication from Resident Programs. 2. The communication in every part must be sent to the IRC server to confirm the source of message sent to the chat rooms. The main purpose of communication is to maintain old relationships and make new relationships. However, the communication on IRC networks is limited to various reasons-the mere means of communication in text, time of Internet connection and shared communication space by having several chat partners at the same time. 3. The language used to communicate on IRC networks have many unique characteristics, for instance, phoneme and spelling, level of language, usage of special language patterns and characters to express feelings, and controls of language used in communication.