The thermal stability of bulk Ti3SiC2 in high-purity nitrogen was investigated. It was surprising to observe that Ti3SiC2 underwent rapid and catastrophic disintegration above 1300 degrees C, although this material was thermally stable below this temperature. This degradation was unexpected and extremely serious, and has been termed "Ti3SiC2 pest." This phenomenon was related to the volume change associated with the formation of mixtures of TiCx, Ti(C, N)(x), and TiN, which caused internal tensile stresses and cracked the resulting layers. "Ti3SiC2 pest" could be prevented by increasing oxygen partial pressure in nitrogen.