A kind of semiaromatic polyamide, poly(dodecamethylene terephthalamide) (PA12T) was synthesized via a polycondensation reaction of terephthalic acid and 1,12-dodecanediamine. The structure of prepared PA12T was characterized by Fourier transform infrared spectroscopy, proton nuclear magnetic resonance (1H-NMR), and elemental analysis. The mechanical properties of PA12T were also studied. The thermal behavior of PA12T was determined by differential scanning calorimetry, thermogravimetric analysis, and dynamic mechanical analysis. Pyrolysis products and thermal decomposition mechanism of PA12T were analyzed by pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS). Melting temperature (Tm), glass transition temperature (Tg), and decomposition temperature (Td) of PA12T are 310°C, 144°C, and 429°C, respectively. The Py-GC/MS results showed that the pyrolysis products were mainly composed of 32 kinds of compounds, such as benzonitrile, 1,4-benzenedicarbonitrile, N-methylbenzamide, N-hexylbenzamide, and aromatic compounds. The major pyrolysis mechanisms were β-CH hydrogen transfer process, main-chain random scission, and hydrolytic decomposition. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011.