We have developed a novel method to construct porous hydroxyapatite (HA) by dual-phase mixing—in other words, generating a porous ceramic body and pore-forming template simultaneously. The technique is based on mixing two immiscible phases: HA slurry and polymethylmethacrylate (PMMA) resin. Naphthalene particles are necessary when greater porosity (>50%) is wanted. After shaping in a mold, the mixture is subjected to polymerization, drying, pyrolysis, and sintering. The porous HA has been thoroughly characterized with Fourier transformation infrared spectrometry, X-ray diffractometry, environmental scanning electron microscopy coupled with energy-dispersive X-ray analysis, and image analysis. The demanding specifications for bone ingrowth are met: (i) the size of pores and their fenestrations are adjustable, ∼80% within 300–800 μm; (ii) uniform and isotropic porous structure is observed in three directions; (iii) pores are fully interconnected throughout; (iv) the porosity is adjustable up to 60%; and (v) sufficient mechanical strength is present for cell culture and implantation handling. The porous HA can be applied as either implant material or scaffold for bone-tissue engineering.