The formation of sufficiently large three-dimensional nano/macroporosity in bone scaffolds remains a challenge despite the numerous fabrication methods reported in literature. The presence of such porosity is required for tissue ingrowth and for the concurrent degradation of implanted structure. A new technique of combining the slip casting and polymer sponge methods using the slips with different powders was introduced in the study to prepare hydroxyapatite scaffolds with bimodal pore sizes. This technique provided better control over the microstructures of scaffolds and enhanced their mechanical properties compared to traditional methods. With this technique, we were able to produce scaffolds with mechanical and structural properties that could not be attained by the polymer sponge or slip-casting method alone. The scaffolds were prepared with an open, uniform, and interconnected porous structure with a bimodal pore size of 100–300 μm. The bimodal porous hydroxyapatite scaffold sintered at 1200°C had a large flexural strength of 73.3 MPa and a porosity of 52.5 vol%. These bioscaffolds hold promise for applications in hard tissue engineering.