The purpose of this study is to investigate pre-service teachers' perceptions and their difficulties of mathematics instruction. Pre-service teachers have positive perceptions about teaching students and teaching profession through teaching practicum. In addition, they have perceived that teaching practicum can enhance teaching methods for their students. Especially, they suggested that cooperating teachers' instruction and mathematics teachers and their colleagues' classroom observation are important factors to improve their teaching methods. In other hands, they have difficulties in application of questions encouraging mathematical thinking, attention concentration considering students' interest and planning and performing for mathematics instruction class according to levels of students' study abilities. Based upon this study's findings, teacher education institutes should make efforts to alleviate difficulties in mathematics instruction through effective teaching practicum such as regular reflection activities for their classes, programs development associated with schools, pre-training and education programs for guidance teachers.