Disclosed are cationic photocurable compositions with improved shelf life stability. The thermally stable compositions comprise at least one cationically polymerizable compound, for example an epoxy compound, at least one onium salt photoinitiator and at least one compound selected from the group consisting of the organic phosphorus stabilizers and the hindered nitroxyl stabilizers. Also disclosed is a cationic photoinitiator composition comprising at least one onium salt photoinitiator and at least one compound selected from the group consisting of the organic phosphorus stabilizers and the hindered nitroxyl stabilizers.