Abstract An attempt was made to use indentation approach to determine the fracture toughness of phase-separated glasses having particulate microstructure. The samples selected for study were lead borate glasses whose composition lies in the immiscible region of the PbOB 2O 3 system. Indentation fracture experiments were performed on the polished surface of the specimens using a Vickers microhardness tester. The extent of surface traces of well-developed half-penny-like cracks growing from the corners of Vickers indents were measured. Fracture toughness values were then evaluated based upon the established indentation fracture mechanics. These values were compared with fracture toughness data obtained for the same glasses by the conventional three-point bending technique. It was found that Vickers indentation testing can be an efficient method for fracture toughness evaluation of opaque two-phase glasses.