Epoxy-novolac resins were synthesized by modifying a commercial novolac resin with epichlorohydrin. These epoxy-novolac resins were characterized and further modified with different contents of bis(benzo-1,3,2-dioxa-borolanyl)oxide or bis(4,4,5,5-tetramethyl-1,3,2-dioxa-borolanyl)oxide. The boron-containing epoxy-novolac resins were autocatalytically crosslinked or crosslinked with BF(3)MEA and their thermal stability and flame retardancy were determined by thermogravimetric analysis and limiting oxygen index (LOI) values. These LOI values for the bis(benzo-1,3,2dioxa-borolanyl)oxide derivatives were higher than the boron-free novolac resins, which shows the benefit of the presence of boron. To test the role of boron in the enhancement of flammability, scanning electronic microscopy and energy-dispersive X-ray spectroscopy images were made. (c) 2006 Wiley Periodicals, Inc.