Debate can be used as a tool to help students’ in language learning process. Through debate students can improve their speaking skill. This research is aimed to find out the roles of English debate activity in developing students' English speaking skill and to find out the aspects of joining English debate activity in developing students' English speaking skill as perceived by students'. This research used a descriptive qualitative method. The data were gained by interviewing four college students about the experience in debate activity at an Islamic private university of Yogyakarta. The results show that there are five roles of debate activity in developing students’ English speaking skill. The roles to boost students’ confidence in speaking, motivate students to speak English, develop students’ critical thinking in speaking, and add the students’ knowledge. Furthermore, there are four aspects of joining English debate activity as perceived by students. They are to improve students’ vocabulary, grammar, pronunciation, fluency, expressive devices.