The aim of this longitudinal study was to examine prospective teachers' mathematics teaching efficacy belief during their enrollment in teacher education program and at the end of their first year of teaching. In addition, the factors that enhance or inhibit participants' efficacy belief and how these factors affect their mathematics teaching efficacy when they become inservice teacher were investigated. Mixed research design was used in which data were collected through longitudinal survey and electronic interviews. Findings revealed that prospective teachers' mathematics teaching efficacy beliefs increase during their enrollment in teacher education program but decrease during their first year of teaching. In addition, classroom management, communicating with student, communicating with parents, mathematical knowledge for teaching, material usage, and textbook usage are the factors that enhance or inhibit teachers' efficacy beliefs during their first year of teaching.