Résumé : For more than a decade now, research is done on a 1 kN lab-scale Hybrid Rocket Motor (HRM) at the Université Libre de Bruxelles (ULB), in close cooperation with the Royal Military Academy (RMA). As opposed to liquid or solid rocket motors, HRMs operate with a liquid or gaseous oxidizer which is injected in a combustion chamber containing a solid fuel. Since the ULB-HRM research has only been experimental so far, the addition of a numerical dimension seems very opportune. In this work, the first Computational Fluid Dynamics (CFD) model of the ULB-HRM is developed, validated, and applied. Doing so, a numerical dimension and a predictive capacity are added to the research. The model is a two-phase flow model both in oxidizer and in fuel, which is very uncommon in literature on HRM modeling. Such an approach leads to accurate results and a series of insights which are reported in the work. The average deviations between the numerical and the experimental results are +1.1% in chamber pressure and +5.0% in thrust. The CFD model forms the foundation for future numerical investigations of the ULB-HRM, and it contributes to any HRM research in which a two-phase numerical approach is considered.