As part of a large-scale thermophysical property measurement project, the decomposition kinetics of propylcyclohexane was investigated. Decomposition reactions were performed at 375, 400, 425, and 450 degrees C in stainless steel ampule reactors. At each temperature, the extent of decomposition was determined as a function of time by gas chromatography. These data were used to derive first-order rate constants for the decomposition of propylcyclohexane. Decomposition rate constants ranged from 3.66 x 10(-7) s(-1) at 375 degrees C to 8.63 x 10(-5) s(-1) at 450 degrees C. Among other things, these rate constants are useful for planning property measurements at high temperatures. Based on the amount of time required for 1% of the sample to decompose (t(0.01)), we found that allowable instrument residence times ranged from about 8 It at 375 degrees C to about 2 min at 450 degrees C. The kinetic data were also used to determine Arrhenius parameters of A = 2.56 x 10(16) s(-1) and E-a = 283 kJ . mol(-1). In addition to the decomposition kinetics, we have also done a GC-MS analysis in order to identify the most abundant decomposition products.