By acid-catalyzed and alkali-catalyzed pyrolysis gas chromatography (PyGC), we analyzed synthetic fibers such as acrylic, 6-nylon, 6, 6-nylon, polyester, polyurethane, vinylon, polypropylene, acetate and viscose rayon, and natural fibers such as cotton, wool, silk and hemp. Fibers were analyzed in the presence of phosphoric acid, hydrochloric acid or sodium hydroxide aqueous solution as catalysts using a gas chromatograph and a gas chromatograph/mass spectrometer equipped with a Curie point pyrolyzer. These three catalysts produced increasingly some specific volatile substances from condensation-polymerized fibers such as cotton, hemp, viscose rayon, wool, silk, 6-nylon and 6, 6-nylon, compared with conventional non-catalyzed pyrolysis. From addition-polymerized fibers such as vinylon and acrylic, however, these catalysts produced decreasingly some specific volatile substances from the fibers. This results suggested that forensic identification of minute unknown fiber samples should be performed in the combination of conventional non-catalyzed and acid-catalyzed or alkalicatalyzed PyGC. Furthermore, we investigated the mechanism of acid-catalyzed and alkali-catalyzed pyrolysis, using deuterium-labeling acid and alkali in D2O.