Instant Messaging ¡]IM¡^ has becomes an important tool of communication. Currently, eighty percent of the Internet users use IM to communicate each other. This study uses the dimensions of performance expectancy and effort expectancy of the Unified Theory of Acceptance and Use of Technology and the interpersonal communication need to investigate factors that influence IM acceptance. There are 211 completed questionnaires were returned and analyzed. It¡¦s found that performance expectancy, effort expectancy, and interpersonal communication show significantly positive and significant impacts on IM users¡¦ intention. The intention significantly and positively affects their IM usage. According to the results, it¡¦s suggestted that IM software should make the IM more user-friendly and the software interface is not too complicated, so that users might feel that IM software is easy to use.