Effects of mullite on the structure, microhardness and machinability of fluorphlogopitemullite glass-ceramics were investigated by X-ray diffractometry (XRD), differential scanning calorimetry (DSC), scanning electron microscopy (SEM) and microhardness tester. Results show that the microhardness and machinability are related closely to its microstructure. The microhardness decreases remarkably with the increase of crystallization and the formation of interlocking structure. The addition of mullite can decrease the size of mica crystals, which results in the spoil of interlocking structure. The microhardness of the glass-ceramics is slightly increased and then decreased with the addition of mullite. When the content of mullite is 15wt%, the glass-ceramics shows good machinability after reheated at 1200°C for 2h.