Fracture toughness of epoxy was determined by quantitative fractography, one of the techniques for brittle materials based on fracture mechanics. Two different epoxy systems, an anhydride-cured and an amine-cured epoxy based upon diglycidyl ether of bisphenol A (DGEBA) were studied. Epoxies with different average molar mass between crosslinks (M-c) or crosslink density were prepared by varying the cure profiles. The materials were characterized using differential scanning calorimetry (DSC), dynamic mechanical spectroscopy (DMS), and density measurements. Optical microscopy was used to measure the dimensions of the different regions on the fracture surfaces of unnotched samples that were tested to failure under tension. The fracture toughness values were calculated from the relationship between the measured sizes and fracture stress. Epoxies with lower M-c values or higher crosslink densities have lower fracture toughness values.