Residual monomers in poly(acrylonitrile-co-butadiene-co-styrene) (ABS) were extracted using direct thermal desorption as well as solvent extraction, and were analyzed using gas chromatography (GC). Headspace sampling and liquid injection were employed as an injection method. For the solvent extraction/liquid injection method, the solvent peak covered the residual monomer peaks. For the solvent extraction/headspace sampling method, the solvent peak was almost not overlapped with the residual monomer peaks, but the peak intensities of the residual monomers were small compared to the liquid injection. Using the direct thermal desorption method, clear chromatograms were obtained. The residual monomers were extracted by heating at $75-150^{circ}C$ for 5 h, and the thermally desorbed materials were injected to GC by headspace sampling. Amounts of the residual monomers increased with increase of the heating temperature. The recommendable method to analyze the residual monomers in ABS was that the extraction method was direct thermal desorption at $150^{circ}C$ for 5 h, and the injection method was headspace sampling.