Size-dependent exciton spin relaxation dynamics in CdTe colloidal quantum dots is studied at room temperature with the cross-polarized heterodyne third-order nonlinear transient grating technique The CdTe exciton spin relaxation reveals a mono-exponential decay behavior with a time constant of 0.1-0.5 ps when the pump-probe photon energy is tuned to be in resonance with the lowest exciton absorption transition (1Se-1Sh). The exciton spin relaxation in quantum dot is mainly governed by the hole spin flip process and ascribed to the transitions between bright-dark exciton fine structure states, i.e. J= 1+2. This finding suggests that the exciton spin relaxation rate in CdTe quantum dot is inversely proportional to the fourth power of quantum dot size.