Phosphate tri (2,6,7-trioxa-1-phosphabicyclo [2.2.2] octane-1-oxo-4-methanol) phosphate (trimer) and its microcapsules with MUF resin shell, respectively, were synthesized. Their structures were characterized by NMR, IR, and SEM analysis. Epoxy resins (EP) were modified with trimer, and its microcapsules to get the flame retardant EP, whose flammability and burning behavior were characterized by UL 94 and limiting oxygen index (LOI). About 20% of the trimer microcapsules were doped into EP to get 30.2% of LOI and UL 94 V-0. Thermal properties of the flame retardant EP were investigated with thermogravimetry (TG) and differential thermogravimetry (DTG). Weight loss behavior and thermal stability were characterized. For EP containing the trimer microcapsules, compared with EP containing trimer, incorporating melamine group into EP decreased weight loss and the maximum weight loss rate, increased the char yield and thermal stability. (C) 2010 Wiley Periodicals, Inc. J Appl Polym Sci 119: 2025-2030, 2011