The purpose of this research was to explore the effect of teachers' mathematical knowledge on self-efficacy for teaching mathematics. The framework of teacher's mathematical knowledge broadened in scope from teachers' common mathematical knowledge, specialized mathematical knowledge, to horizon mathematical knowledge. These three were modeled and integrated into the teaching of the division of fractional numbers. The method used in this research was quasi-experiment that involved 42 teachers of elementary schools. Path analysis was applied to data that included the direct or indirect effects of mathematical knowledge on self-efficacy. Results indicate that horizon mathematical knowledge was statistically significant and positive for self-efficacy for teaching mathematics (=0.657, p=0.000). Significant statistic was also shown in the effect of horizon mathematical knowledge on both common mathematical knowledge (=0.362, p=0.019) and specialized mathematical knowledge (=0.574, p=0.000). However, the effect of both common mathematical knowledge (=0.093, p=0.509) and specialized mathematical knowledge (=0.029, p=0.857) on selfefficacy for teaching mathematics was not statistically so. The importance of building self-efficacy in the current workforce of mathematics teacher through a wide range of training practices for teacher's horizon mathematical knowledge needs further potential directions, accordingly.