Hydroxyapatite ceramics (HA) has been proved to be excellent in biocompatibility and bioactivity. However, limited information is available concerning how HA ceramics affects the maturation of osteoblasts in molecular biological level in vitro. This study examines the mRNA expression and protein production of bone-related genes in osteoblast-like cell line (Saos-2) cultured on HA disks. Saos-2 cells are seeded onto the substrates and cultured for 18 days. Harvested cells are tested for the cell growth rate, expression of mRNAs for osteocalcin and alkaline phosphatase, and protein production of bone sialoprotein and osteocalcin. MTS assay shows that cell proliferates well on HA ceramic substrate. After 9d, bone sialoprotein and osteocalcin protein production in SaPS-2 increases more on HA surfaces than on control material. As bone sialoprotein and osteocalcin are the genes to be highly expressed at the late stage of osteoblast differentiation, this study reveals that after long time culture in HA, HA can induce Saos-2 maturation. The behavior of Saos-2 on HA surfaces revealed in this study provides valuable information for the understanding of the biocompatibility and bioactivity of HA ceramics.