To obtain a novel multifunctional flame retardant material, Triphenyl phosphate (TPP) was used as the capsule material to microencapsulate diatomite/ammonium polyphosphate (Dia/APP). The novel multifunctional material Dia-APP-TPP could effectively improve the flame retardancy of unsaturated polyester resin (UPR). The desired structure of Dia-APP-TPP was clearly observed through Fourier Transform Infrared (FTIR), X-ray Photoelectron Spectroscopy (XPS) and Scanning electron microscopy (SEM). The combustion behavior, thermal property and mechanical performance of UPR/Dia-APP-TPP composites were also investigated. Incorporation of Dia-APP-TPP into UPR greatly enhanced the flame retardancy and thermal stability of the composites. Remarkably, with 20 wt% of Dia-APP-TPP, UPR-2 successfully achieved UL-94 V-0 rating and the LOI value increased from 19.2% to 26.6%. Besides, the CCT test showed that the THR value of UPR-2 decreased by 33.9% compared with that of pure UPR. The results of this study also confirmed that a novel and feasible strategy can be used to obtain a microencapsulation flame retardant. (C) 2019 Elsevier B.V. All rights reserved.