The object of this study is to explore factors affecting customer satisfaction and customer loyalty of instant messenger service. We propose that service qualities (tangibility, assurance, responsiveness, empathy, reliability) affect customer satisfaction of instant messenger service, customer satisfactions do customer loyalty. As moderating factors of the relationship between customer satisfaction and customer loyalty, switching costs are suggested. To accomplish the object of this study data are collected from instant messenger user by survey research. We analyse the research model using structural equation model and moderated multiple regression. The result are as follows: (1) tangibility and responsiveness affect customer satisfaction. (2) customer satisfaction affects customer loyalty. (3) switching costs moderated the relationship between customer satisfaction and customer loyalty.