In this study, we intend to synthesize the new bio-glass composition with fluoride additions, such as CaF2 and MgF2, instead of Na2O in bio-glass ceramic composition based on 45S5 (46.1SiO2-26.9CaO-24.4Na2O-2.6P2O5, mol%). Also, we intend to increase the SiO2 content up to 50 mol% to enhance the mechanical properties. When B2O3 (4 mol%) was added as a Na2O substitution, thermal expansion coefficient was decreased at the sintering temperature (650~950 oC). Compared to the low flexural strength (57±3 MPa) and vickers hardness (4.6 GPa) of sintered bio-glass ceramics without fluoride and B2O3, bio-glass ceramics substituted with 10mol% MgF2 for Na2O showed more higher mechanical properties (flexural strength: 141±5 MPa, vickers hardness: 5.6 GPa). Thermal expansion coefficient of bio-glass ceramics with the ion substitutions (Ca2+, Mg2+ and B3+) was decreased from 16×10-6/oC to 9.4~10×10-6/oC (~400 oC).