Combination of polyurethane and phosphate provides an efficient intumescent flame retardant (FR) system which is not permanent because of the water solubility and migration of phosphate. Microencapsulation has appeared as an alternative way to achieve the permanence of the intumescent flame retardant system. This work deals with the microencapsulation of di-ammonium hydrogen phosphate (DAHP) by polyurethane-urea membrane using an interfacial polymerization method. Chemical and physical structures of the DAHP microcapsules were characterized. According to the thermal degradation analysis, the DAHP microcapsules show characteristics of an intumescent system. (c) 2006 Elsevier B.V. All rights reserved.