Although teachers’ beliefs about mathematics are widely recognized as important influences on instructional decision-making, empirical evidence regarding the role of ontological beliefs in shaping mathematics teaching practices remains limited, particularly in Sub-Saharan African contexts such as Ghana. This study therefore examined whether pre-service mathematics teachers’ ontological beliefs were significant statistical predictors of their mathematics teaching practices. Guided by Ernest's Philosophy of Mathematics Education, the study employed a quantitative cross-sectional survey design involving 312 Level 300 pre-service mathematics teachers from a public university in Ghana. Data were collected using a researcher-developed questionnaire measuring ontological beliefs and mathematics teaching practices and analysed using descriptive statistics, Pearson product-moment correlation, and simple linear regression in IBM SPSS Statistics Version 26. The findings indicated that the participants demonstrated a high level of ontological beliefs regarding the nature of mathematics. Pearson correlation analysis revealed a strong positive relationship between ontological beliefs and mathematics teaching practices (r=.699,p<.001). Simple linear regression further showed that ontological beliefs were significant statistical predictors of mathematics teaching practices (β=.699,p<.001), explaining 48.8% of the variance in instructional practices (R2=.488). These findings suggest that pre-service teachers who perceive mathematics as a discipline characterised by reasoning, exploration, creativity, and discovery are more likely to report instructional practices that promote meaningful mathematical learning. The study concludes that ontological beliefs constitute an important explanatory factor associated with pre-service mathematics teachers reported instructional practices.