In this study, how undergraduates use QQ and how their behavior related to academic purposes in informal setting were examined by interview and content analyze. It was found that QQ was used as a learning supporting tool spontaneously by undergraduate. Learners initiated various learning activities, such as peer-to-peer online help, class discussion and academic document sharing by QQ without any requirement by teachers. In addition, QQ also has emotional and affect impact on participants. Finally, the feature of QQ-"class group" created a new tool for learners to communicate after class and bridge class and off-class management. These findings showed the possibility of public IM as learning supported tool and some problem we should consider when use public IM in learning supporting.