Abstract: Citric acid modified βzeohte(N-β)was prepared via impregnation method. IR showed that citric acid had a function to increase the content of aluminum in β zeolite. the influences of N-β on the thermal stability, flame retardant performance, microstructure, mechanical properties, and processability of ABS/intumescent flame retardant(IFR) system were investigated using the tests of thermogravimetric analysis (TGA)，limiting oxygen index (LOI)，scanning electron microscopy (SEM)，etc.It showed that a lower content N-β had a synergistic effect with intumescent on the flame retardancy,which promoted the formation of stable, continuous and compact char structure at high temperature.When the content of N-βwas 2 wt，the LGI and the mass of residual char of ABS/IFR composites were 31.3%and 24. 86%，respectively. As the content of N-β increased, the impact and tensile strength of the composites increased at first and then decreased.

Key words: acrylonitrile-butadiene-styrene copolymer, β zeolite, citric acid, intumescent flame retardant, synergistic effect