Four fluorcanasite glass-ceramics were fabricated by controlled heat-treatment of as-cast Glasses A-D. These compositions have been reported previously but essentially, Glass A had the stoichiometric composition (Ca5Na4K2Si12O30F4) and Glasses B-D were modified by reducing the Na2O concentration (B), adding excess CaO (C) and P2O5 (D). The latter two compositions have been shown to have promising bioactive response in cell culture and simulated body fluid experiments. Devitrification of the stoichiometric composition resulted in poor mechanical properties with crumbling often observed on machining. As a result, no mechanical data could be obtained. In all modified compositions, heat-treatment between 780 degrees C and 900 degrees C resulted in measurable indentation fracture toughness (IFT) and biaxial flexural strength (BFS). IFT was optimised in Glass C at 800 degrees C (2.53 +/- 0.02 MPa m), but the biaxial flexural strength (BFS) was low, 167 +/- 17 MPa, compared to other compositions. For heat- treated Glass D optimum mechanical properties were obtained at 800 degrees C with BFS and IFT, 249 +/- 23 MPa and 1.95 +/- 0.01 MPa m, respectively. The relationship between the mechanical properties and microstructure is discussed.