Issues about low level of mathematical knowledge for teaching among pre-service teachers has raised the question on the effectiveness of the mathematics teacher education program which has been planned and implemented by the Malaysian Institute of Teacher Education (MITE). This study was conducted to identify factors that affect mathematical knowledge for teaching (MKT) among pre-service teachers in Institute of Teacher Education (ITE). The influence of mathematical belief and opportunity to learn (OTL) have been tested to explain the factors affecting MKT. Using a structured questionnaire together with paper and pencil test adapted from the literature reviewed, data were collected from 105 pre-service teachers in MITE. Data were analysed using SmartPLS version 3.0. The result of the structural equation model indicated that OTL-Practicum (β=0.491, p<0.001) and OTL-Program (β=0.368, p<0.001) has a positive relationship with mathematical knowledge for teaching. Besides that, the result for the impact of OTL on mathematical belief, it showed that OTL-Practicum (β=0.208, p<0.001) and OTL-Program (β=0.243, p<0.001) has a positive relationship with constructivist belief, whereas OTL-Program was negatively related to traditional belief (β=-0.283, p<0.001). Overall, the model explained 53.9% of the variance in mathematical knowledge for teaching. Implications from these findings to the ITE were further elaborated.