The use of online tools such as forum has helped instructors develop courses that are engaging and challenging. However, instructors want to ensure that all students maintain academic integrity when they were assigned to work in an online community. This paper investigated students' perception and behavior of academic integrity in an online discussion forum. Data were collected from 160 students enrolled in a fundamental English course who were assigned to post and respond to the topics in a forum. A survey was administered to measure how students perceived "academic integrity" as well as to investigate students' experience of violating academic integrity. A semi-structured interview was further conducted with the involved participants to find out the reasons behind their performance. The findings revealed that students perceived some misconduct actions as not cheating, leading to behaviors of academic dishonesty. As such, students should be informed more about what they can or cannot do in order not to commit academic dishonesty.