Thermo-osmosis of water through a composite clay membrane consisting of kaolinite and crysotile clay membrane elements in a parallel array has been studied. Water flux in presence of both pressure difference and temperature difference for the parallel composite clay membrane and also for the constituent clay membrane elements has been shown to be adequately described by the usual linear and homogeneous phenomenological equation. The combination rules for the phenomenological coefficientsL₁₁ andL₁₂, representing hydraulic permeability and thermo-osmotic permeability, as deduced from the theory of Kedem and Katchalsky, have been found to be valid. The validity of the combination rules forL₁₁ andL₁₂, in the case of parallel composite membrane has yielded a relationship between the heat of transport of water for the parallel composite membrane and the heat of transport of water for the constituent clay membrane elements.