The pyrolysis behavior of an essence, 4-oxo-beta-damascone, was investigated using an on-line pyrolysis gas chromatography-mass spectrometry (PyGC/MS). In helium atmosphere, the compound was pyrolyzed at 350, 450, 550, 650, 700, and 750 degrees C, separately. The pyrolysis products were directly introduced into GC/MS with 1.03 x 10(6) Pa He and were qualitatively and semi-quantitatively analyzed. At the six pyrolysis temperatures mentioned above, 3, 7, 15, 33, 42 and 45 products were detected and their relative contents were 96.25%, 85.44%, 87.18%, 78.37%, 78.29% and 83.13%, respectively. The results indicated that the pyrolysis temperature directly affected the pyrolysis pattern and the relative content of the products. A total of 54 products were identified, including beta-damascone, 4-oxo-beta-ionone, 3,4,4-trimethyl-2-cyclohex-en-1-one and 2,5,5-trimethyl-cyclohex-3-en-1-one. At 550 degrees C, only a small portion of the parent compound was pyrolyzed. At 750 degrees C, the compound was completely pyrolyzed, with a conversion of 99.74% and 45 products were given. Moreover, with the elevation of the pyrolysis temperature, complex pyrolysis products were formed, and harmful substances, such as benzene, toluene, anthracene and phenanthrene were identified. According to the relative content and the category of the pyrolysis products, the pyrolysis mechanism of 4-oxo-beta-damascone is further discussed with the conclusion that the pyrolysis of this compound might take place via 4 different pathways. The investigation gave an exemplification for the transfer behavior of tobacco essence in the cigarette burning process, and provided a reliable theoretical foundation for the perfume reinforcement technology in tobacco products, contributing to the development of cigarette products with better aroma and taste.