The simultaneous analyses of NMP and DMAc in synthetic fibers that have been regulated recently due to their human hazard properties were studied by both a conventional GC-MS method and a thermal desorption(TD)-GC-MS method that uses Py-GC-MS instrument using the thermal desorption function. Method validation characteristics such as linearity, precision of peak area and retention time, limit of quantification on their determination using a new TD-GC-MS method were found to be acceptable according to the well-recognized method validation guidelines and the current regulation limit. Recovery ratios of DMAc from the spiked synthetic fibers were estimated to be 95.2% to 97.1% with Soxhlet extraction using methanol as measured by GC-MS. Residual amounts of NMP and DMAc in commercial meta-aramid, polyester, and spandex fibers were measured by and GC-MS and TD-GC-MS, respectively and showed a good correlation between two methods with the ratio of 85.5% to 119%. Results of this study suggested that the TD-GC-MS analysis can provide both a good screening and a quick determination of NMP and DMAc in synthetic fibers without any solvent extraction of fiber samples that is a routine and time consuming pretreatment in the conventional GC-MS analysis.