The thermal decomposition of four alkanethiols was investigated in this paper. The test was processed in a pressure reactor at 200-400 degrees C. GC/ MS and GC/SCD were used to detect the products of thermal decomposition. The result indicates that the alkane groups of alkanethiols have great influence on the thermal stability of alkanethiols. N-butylthiol, isobutylthiol and n-hexylthiol begin to pyrolyse at about 250 degrees C and more than 75% decomposes at 400 degrees C after being maintained for 4 h. However, tert-octylthiol can be broken down at lower temperature below 200 degrees C and almost 75% decomposes at 250 degrees C after 4 h. The main product of thermal decomposition is H2S and a free radical reaction is used to explain the decomposition mechanism. (C) 2005 Elsevier B.V. All rights reserved.