A novel flame retardant zinc methylethylphosphinate (Zn(MEP)) was used to fill epoxy resins (EPs). The structure of Zn(MEP) was conformed with Fourier transform infrared, hydrogen nuclear magnetic resonance and phosphorus nuclear magnetic resonance, and X-ray fluorescent and X-ray diffraction. The flammability, decomposition behavior, and glass transition temperature (Tg) of cured EP/Zn(MEP) were investigated. Zn(MEP) is stable below 406°C. EP containing 20 phr of Zn(MEP) achieves 27.5% of limiting oxygen index and UL-94 V0 rating. Scanning electron microscopy-energy-dispersive X-ray and Fourier transform infrared spectroscopy investigations show that a condensed char layer with carbon-rich and phosphorus-rich components was formed during heating Zn(MEP)/EP, the atomic ratio of P to Zn on the surface of the char is reduced compared with the initial sample. The P-rich components and lower atomic ratio of P/Zn on the char surface implies that the Zn(MEP) acts in both condensed phase and gas phase. TGA investigation shows that there are interactions between Zn(MEP) and EP when they are copyrolyzed. The interactions lead to a modification in degradation process and promote the char forming. Compared with aluminum diethylphosphinate Zn(MEP) filled EP shows lower limiting oxygen index but higher Tg. In addition, the interactions between polymer and additive are different when aluminum diethylphosphinate instead of Zn(MEP) is added into EP. Copyright © 2013 John Wiley & Sons, Ltd.