By applying the theoretical model of Mohamed and Langdon [1] the activation energy for high temperature plastic deformation of TiCx single crystals as a function of C:Ti atom ratios is obtained. It is found that the values for the activation energy at the critical resolved shear stress are lower than the lattice self-diffusion data for carbon, except for x = 0.75. At this concentration a peak in the activation energy, 560 KJ, mol(-1), which is about 75% of that for lattice self-diffusion of Ti in TiC, appears. This situation is due to an ordering hardening caused by a contraction of the "window", formed by titanium atoms, through which the carbon atom diffuses. It is concluded that the x-dependence of the activation energy can be understood by considering that during deformation the diffusion processes of carbon and titanium atoms are coupled.