Micron-spherical　granules　of　hydroxyapatite　(HAp)　nanoparticles　were　prepared　by　powder　granulation　methods.　Through　subsequent　sintering,　porous　HAp　microspheres　with　tailored　pore　and　grain　framework　structures　were　obtained.　Detailed　microstructure　investigation　by　SEM　and　TEM　revealed　the　correlation　of　the　pore　structure　and　the　necking　strength　with　the　sintering　profiles　that　determine　the　coalescence　features　of　the　nanoparticles.　The　partially　sintered　porous　HAp　microspheres　containing　more　than　50%　porosity　consisting　of　pores　and　grains　both　in　nano-scale　are　active　in　inducing　the　precipitation　of　HAp　in　simulated　body　fluid.　The　nano-porous　HAp　microspheres　with　an　extensive　surface　and　interconnecting　pores　thus　demonstrate　the　potential　of　stimulating　the　formation　of　collagen　and　bone　and　the　integration　with　the　newly　formed　bones　during　physiological　bone　remodeling.