High-resolution pyrolysis gas chromatography-mass spectrometry (HRPyGC-MS) and Fourier transform infrared spectrometry (FTIR) were used to study the structures of the chlorinated natural rubbers (CNR) prepared by two different processes. The results indicate that the fine structures of CNR prepared from "latex" and "solution" processes are different, whereas their basic structures are similar. The molecule of CNR from the "latex" process contains a few carboxyl and carbonyl groups. The rings on CNR molecular chains should be hexatomic rings. The optimum pyrolytic temperature for CNR is 445degreesC, with an available range from 386 to 590degreesC. The characteristic pyrolytic products are cyclohexane homologues.