In this study, the effect of MgF2 additive on the mechanical properties of hydroxyapatite (HAp)/zirconia composites was investigated. As a fluoride additive, MgF2 was added to HAp/zirconia composites for the suppression of phase decomposition from HAp to tricalcium phosphate (TCP). Due to the dissolution of MgF2 at the phase decomposition temperature of HAp, the phase decomposition of non-stoichiometric HAp was suppressed. When MgF2 (5, 10 vol%) was added to HAp/zirconia composites, the decomposition of HAp was completely suppressed below 1400oC due to the ion substitution F- of for OH- in the HAp crystal structure. The flexural strength and Vickers hardness of composites was revealed more higher values compared with the MgF2-free composites.