The use of humor in EFL classroom has widely discussed in previous research as a useful means of reducing affective barriers to foreign language acquisition. This study aimed at investigating the effectiveness of humor on EFL students’ engagement in classroom activities, and also examining the perceptions of both students and teachers of their use of humor in the classroom. An observation process was made in four English classes including 126 English – majored seniors and four instructors in Can Tho University, Vietnam. The students were asked to complete the questionnaire on their ideas about the use of humor in the classrooms and its effects on their engagement in activities. A set of interviews with 15 students among the student participants and four instructors was also conducted for the data collection. The results revealed that classroom humor usage had noticeable positive influences on concentration, willingness to participate in class activities, and enjoyment in learning and create a comfortable environment conducive to learning.