The equilibrium constant for the methylcyclohexane-toluene system has been experimentally determined due to a lack of fit appearing in kinetic evaluations when using literature values for the equilibrium constant. The most recent literature value of K-eq(T=650 K)=4.61 +/- 0.04 x 10(9) kPa(3) due to J. Akyurtlu and W.E. Stewart (J. Catal. 51, 101 (1978)) was redetermined to a value of K-eq(T=650 K)= 3.60 +/- 0.05 x 10(9) kPa(3) with isothermal experiments using methylcyclohexane and toluene feeds separately.