Objectives: The study aimed to evaluate the biocompatibility of nano-hydroxyapatite or biphasic nano-hydroxyapatite/ß-tricalcium phosphate with two different ratios(HA60:TCP40, HA70:TCP30) in vitro. Methods: The nanoHA (HA100) and biphasic calcium phosphate (nanoHA/ß -TCP) with two different ratios of nanoHA/ß-TCP (HA70/TCP30, HA60/TCP40) were prepared and cultured in osteoblast cell line MC3T3-E1 (ATCC). Cell loading and proliferation were assessed using a WST-1 colorimetric assay. Cellular morphology and adhesion to the scaffolds and cell viability were assessed optically using SEM. The alkaline phosphatase assay and osteocalcin assay were used to detect the early and late stage of osteoblastic cell differentiation. Results: Results showed that osteoblasts were attached to the surfaces of all nano HA and HA/TCP well as seen by SEM observation. Cell proliferation from WST-1 was increased higher on Day 3 than Day 1 in all groups except HA60 which was slightly stable but HA 60 showed higher cell numbers than the other two groups on the first day but no significance. ALP activity also showed the same profile as WST-1 that HA60 enhanced better activity than the other groups on both Day 1 and 3 but activity on both days were comparable whereas the other two groups had increased activity on Day 3. The osteocalcin production on Day 21 was opposite to ALP activity that HA70 presented the highest value which was comparable to HA100, while HA60 showed the lowest level of osteocalcin production. Conclusions: It can be concluded that higher TCP ratio enhanced better cell proliferation in the early phase of cell differentiation while higher ratio of HA yielded better osteocalcin production in the late state of osteoblast differentiation. Keywords: biphasic cacium phosphate, biocompatibility, nanohydroxyapatite, osteoblast, tricalcium phosphate