The active fracture modes in glass-ceramics, produced by controlled crystallization from three starting vitreous products containing PbO and SiO2, were studied and compared. The goal was to examine the active fracture modes in PbO-rich glass-ceramic materials, where the main glass former was PbO, and compare these results with those reported in the literature, where the main glass former was SiO2. The influence of composition, shape and mean size of the ceramic phase on the active fracture modes of the glass-ceramics was also examined. It was observed that the microhardness and fracture toughness of the starting vitreous products decrease with increasing PbO content. Increase in the relative amount of SiO2 resulted in a decrease of the percentage of the ceramic phase. Glass-ceramics with higher PbO content showed typical behaviour of high toughness material, i.e. intergranular fracture mode, with lower microhardness value. Glass-ceramics with lower PbO content showed typical behaviour of high-strength material, i.e. transgranular fracture mode, with higher microhardness value.