Porous hydroxyapatite (HA) artificial bone scaffolds were prepared via the freeze-gel casting process in order to improve their mechanical strengths. As a porogen, various volumes of poly (methyl methacrylate) (PMMA) powders were added to obtain high porosity, such as in cancellous bone. After fabrication, the porous and mechanical properties of the scaffolds were examined. The HA60 scaffold, with a porosity over 80%, had proper compressive strength and modulus and satisfied the range of properties of cancellous bone. Moreover, it was found that the investigated mechanical properties were affected by the scaffolds’ porosity. However, a section was found where the compressive strength was high despite the increase in the porosity. Specifically, HA30 had a porosity of 62.9% and a compressive strength of 1.73 MPa, whereas the values for HA60 were 81.9% and 3.23 MPa, respectively. The results indicate that there are factors that can preserve the mechanical properties even if the porosity of the scaffold increases. Therefore, in this study, various parameters affecting the porous and mechanical properties of the scaffolds during the manufacturing process were analyzed. It is expected that the improvement in the mechanical properties of the artificial bone scaffold having a high porosity can be applied to tissue engineering.