The standing grown of academic self-efficacy as a theoretical framework of the independent contributor to task performance of language skills such as speaking has been widely recognized. Considerable amount of researches has also found self-efficacy in EFL context is still roughly challenging. The present research attempts to explain the speaking self-efficacy of 35 EFL students of a pre-service teaching program who enrolled in an EFL speaking advanced class. The result showed the average percentage of student's self-efficacy in the mastery of speaking skills was 79% which was high. The highest point of those questionnaires was students; belief in their personal ability in the mastery of speaking skills (82%). while the lowest point of questionnaires was factors' influencing students' in public speaking in EFL classroom setting (77%). The average percentage of students' self-efficacy in the mastery of speaking skill can grow with effort was categorized as high scale (79%). This research also revealed that students' sources of self-efficacy based on their positive experiences of task accomplishments, observing role model performances, verbal persuasions, their effort, persistence/resilience that they exerted when obstacles arise, and emotional states. The Self-efficacy level of one student with another's was different despite having the same score and it has nothing to do with gender. Individuals with high levels of self-efficacy approach difficult tasks as challenges to master rather than as threats to be avoided.