The performances of rubber-toughened polymers like acrylonitrile-butadiene-styrene (ABS) are strongly affected by the type and amount of rubber phase. Characterization of rubber phase is an effective method to predict and control the physical and mechanical behaviors of ABS materials. In this work, different methods have been employed to determine the amount of rubber phase in ABS polymers. The first method was based on thermogravimetry using a particular step degradation of the polymer. In the second method, characteristic absorption bands in the Fourier transform infrared spectra were used to make a calibration curve to determine the rubber content of unknown ABS samples. The third method was based on variation of heat capacity of ABS polymers with increasing the rubber phase content. In the fourth method, a two-step solvent extraction followed by centrifuging was used to separate the rubber particles of different ABS samples. Separation of hardened rubber particles was used to study the size and size distribution of rubber particles. (C) 2009 Wiley Periodicals, Inc. J Appl Polym Sci 114: 1908-1913,2009