The aims of this study were to find out the factors contributing to students’ speaking ability and the most dominating factor at the fourth semester students of English Language Education Department of Universitas Muhammadiyah Purwokerto. The subjects of this study were 14 students who have a high score in speaking. Then, the method of this study is survey. To collect the data, researcher used questionnaire and interview as the instruments. The result showed that they were 9 factors contributing to the students’ speaking ability. They are intelligence, attention, interest, aptitude, motivation, family factor, teaching method, discipline system, and school facilities. The most dominating factor which contributed to the students’ speaking ability was motivation. Motivation had the highest percentage among the others factors with percentage 88.69%.