Mono-phase ceramics of monticellite (CaMgSiO4) were successfully synthesized by sintering sol-gel-derived monticellite powder compacts at 1,480 degrees C for 6 h. The mechanical properties and the coefficient of thermal expansion (CTE) of the monticellite ceramics were tested. In addition, the bioactivity in vitro of the monticellite ceramics was evaluated by investigating their bone-like apatite-formation ability in simulated body fluid (SBF), and the biocompatibility in vitro was detected by osteoblast adhesion and proliferation assay. The results showed that the bending strength, fracture toughness and Young's modulus of the monticellite ceramics were about 159.7 MPa, 1.63 MPa m1/2 and 51 GPa, respectively. The CTE was 10.76x10(-6) degrees C(-1) and close to that of Ti-6Al-4V alloy (10.03x10(-6) degrees C(-1)). Furthermore, the monticellite ceramics possessed bone-like apatite-formation ability in SBF and could release soluble ionic products to significantly stimulate cell growth and proliferation. In addition, osteoblasts adhered and spread well on the monticellite ceramics, which indicated good bioactivity and biocompatibility.