Recent surrogate diesel fuel mixture development identified the need for a multiply substituted, low cetane number, high molecular mass monocycloalkane component. On the basis of a thermophysical property evaluation and prediction, 1,3,5-triisopropylcyclohexane was chosen to serve this need. This fluid is not commercially available; therefore, very few thermophysical property measurements exist, and the thermal decomposition kinetics have not yet been investigated. In this work, we study the thermal decomposition kinetics of 1,3,5-triisopropylcyclohexane between 350 and 425 C. The decomposition reactions were performed in stainless-steel ampule reactors. At each temperature, the extent of decomposition as a function of time was determined by analyzing the thermally stressed liquid phase by use of gas chromatography. These data were used to derive pseudo-first-order rate constants that ranged from 2.38 x 10(-7) s(-1) at 350 degrees C to 7.28 x 10(-6) s 425 degrees C. The Arrhenius parameters of the thermal decomposition of 1,3,5-triisopropylcyclohexane were measured to be A = 5.67 x 10(16) s(-1) and activation energy E-a = 279 kJ/mol. These parameters can be used to estimate decomposition rates at other temperatures and are critical to the successful application of 1,3,5-triisopropylcyclohexane in experimental and modeling studies of surrogate diesel fuels.