Medical applications of calcium phosphate biomaterials are limited because of poor mechanical properties and acute inflammation reactions which take place occasionally in the clinic. To increase the usefulness of calcium phosphate biomaterials it is necessary to improve the mechanical properties and biological character. Processing and characterization of porous hydroxyapatite (HA) and dense composite (HA-Spinel) biomaterials have been performed in the present research. Biocompatibility of these biomaterials has been examined in vitro using human and rat immortalized osteoblast cells, and the advantages and limitations of cell culture biocompatibility tests are discussed. X-ray analysis of material structure demonstrated that after sintering at 1450°C, HA-Spinel was changed into tricalcium phosphate (TCP)-Spinel phase structure. Mechanical properties testing showed that the bending strength and compressive strength of HA may be improved by adding Spinel. Biocompatibility examination demonstrated that both human and rat osteoblast cells anchored to the surface of the porous and dense biomaterials in a short time, and subsequently, grew and proliferated normally on the surface of these biomaterials. Cytotoxicity evaluation in vitro by studying material extracts demonstrated that compared with the control group of cells cultured on polystyrene, HA-Spinel possessed slight toxicity. Cell growth in HA-Spinel first extracts was slightly impaired. Tritium labeling and immunofluorescent analysis proved that human osteoblast cells and rat osteoblast cells have normal expression of collagen synthesis on the above biomaterials. Confocal laser scanning microscopy (CLSM) observation showed that collagen fibers were produced on these materials, and the amount of the collagen synthesized on the materials increased with culture time. Subsequent analysis indicated that both HA and HA-Spinel can strongly adsorb serum and albumin proteins from culture media and the amount of protein adsorption was proportional to the porosity in the materials. Protein adsorption on the material surface was saturated usually in 2-4 hours, and 1/3-1/2 of the total protein adsorption was achieved in several minutes. In vitro assay also confirmed that human and rat osteoblast cells can be applied as an in vitro model to evaluate the biocompatibility, cytotoxicity and other biological characteristics. Compared with human osteoblast cells, rat osteoblast cells have a greater proliferation rate. In normal conditions, the proliferation rate of the rat osteoblast cells is 2-4 times that of the human osteoblast cells and for this reason rat osteoblasts seem more sensitive to material extracts.