Experimental results for the measurement of hydrodynamic permeability, electro-osmotic velocity, electro-osmostic pressure and streaming potential for different aqueous solutions of urea and thiourea across the cation-exchange membrane (Indion 236, Sd fine chemicals, India) at 30 °C and voltages up to 25 V are reported. The results have been analysed in the light of thermodynamics of irreversible processes. The cation-exchange membrane has been characterised in terms of effective cross-sectional area, equivalent pore radius, and frictional coefficient. The permeability coefficient L P , has been found to be independent of the hydraulic pressure but is a characteristic property of the membrane and depends upon the concentration of the solute. The reflection coefficient σ, has also been evaluated. Onsager's reciprocity relation has not been found to hold well and this may be attributed to the higher polarization in case of electro-osmosis and also to the highly charged character of the membrane. The efficiencies of maximum electro-kinetic energy conversion took place at half the value of the electroosmotic pressure in each case but the value of maximum energy conversion has been found to be different in both cases thereby also indicating the non-validity of Onsager's reciprocity relation.