In this article, an organically modified zinc aluminum layered double hydroxide (OLDH) was prepared by a facile and effective method. The aim for preparing and decorating LDH is to improve the dispersion of OLDH particles in polypropylene (PP). Fourier transform infrared (FTIR) spectra and X-ray diffraction (XRD) spectra have verified the feasibility for preparing OLDH. In contrast with LDH, the hydrophobicity of OLDH was obviously changed after introduction of sodium dodecyl benzene sulfonate. Together with melamine phytate/dipentaerythritol (MPA/DPER), OLDH was introduced into PP by melt blending. Surprisingly, the synergistic effect of OLDH and MPA/DPER was obviously found in flame-retarding PP. When the content of MPA/DPER and OLDH are 27 phr and 3 phr, the limiting oxygen index value of PP composites is 30.5% and samples can pass UL-94 V-0 rating. Thermogravimetric analysis demonstrates that the participation of OLDH can further enhance the thermal stability of PP/MPA/DPER. Moreover, the surface morphology and chemical structure of PP composites after combustion were systematically analyzed by optical photos, SEM, FTIR spectra, and X-ray photoelectron spectroscopy spectra, respectively. The results reveal that the reinforcing effect of OLDH for char layers structure becomes the main reason for improving the flame retardancy of PP composites. Based on abovementioned analysis, a potential synergistic flame retardant mechanism was primarily proposed. POLYM. ENG. SCI., 2019. (c) 2019 Society of Plastics Engineers