The clay is treated with a reducing agent and an acid so as to obtain a clay containing various metal components with a variable-valence state. Then, the clay is coprecipitated with natural rubber (NR) latex to prepare a vulcanized NR/clay composite. The degradation process of the NR/clay composite under hot air condition was studied dynamically by using a Fourier transform infrared spectrometer attaching an in situ sample cell and was also investigated using the TGA method. The test result obtained from the infrared spectrometry indicated that under low decomposition temperature, the decomposition products of the test samples mainly are ethylene, low molecular olefinic hydrocarbon, and carbonyl compounds. As the decomposition temperature rises, the low molecular olefinic hydrocarbon content decreases, the olefine with longer chain is formed, and a lot of alkane decomposition products are formed at the same time. When the content of the metal components with a variable-valence state in clay such as Cu, Mn, Co-,Co- and Fe increases, the oxidation products containing the carbonyl group, the olefinic hydrocarbon, and CO2 in the decomposition product of the test sample also increase. The TGA result clearly shows a shoulder peak that appears by the side of the main peak on the DTG curve of NR/clay composite. With the increase in the content of metal components with variable-valence state in clay, the initial degradation temperature of the test sample (T-0), the degradation peak temperature (T-p1), and the final degradation temperature (T-f1) in first-stage reaction, as well as the degradation peak temperature (T-p2) and the last final degradation temperature (T-f) in second-stage reaction of all the test samples more or less shift to the direction of low temperature; besides, the activation energy (E) of the reaction of the test samples more or less decreases. This means that the metal components with variable-valence state promote the oxidative degradation of the clay-rubber masterbatch. Q 2006 Wiley Periodicals, Inc.