Nanohydroxyapatite (n-HA) has been widely used as a bone graft material. In contact with biological fluids, n-HA should be reactive, resorbable, form an bone-like apatite layer on their surfaces, and enhance osseointegration. The release of Ca, P, and O in SBF predicted the formation of bone-like apatite layer. Therefore, this study aims to investigate the physicochemical properties of nano-HA powder during the SBF immersion in vitro. The n-HA powder was immersed in SBF for 24, 48 hours, 7, 14, and 28 days. The swelling ratio, pH, FTIR, and SEM-EDX were analyzed pre-and post-SBF immersion. The n-HA powder showed excellent hydrophilicity and a stable pH, even though there was a pH decrease in 28 days. The carbonate and phosphate functional groups were found through FTIR, in line with the ion composition changes and increase of the Ca/P ratio shown on EDX. Both mean weight percentages (%) of Ca and P increased during 14 days of SBF immersion (16.15 to 27.27; and 8.57 to 11.68, respectively). The other functional groups on the n-HA are PO3 −, CO2 −, O-H, C=H, and COO. In conclusion, the n-HA powder presents good physicochemical properties that indicate the formation of an apatite bonelike layer and is promising as a bone graft material.