It is experimentally shown that the stability of aqueous foams can be significantly enhanced by the addition of a small amount of water-soluble polymers. Such enhancement is attributed to the retardation both in the rate of drainage and in the rate of interbubble gas diffusion. Addition of water-soluble polymer increases the bulk viscosity and thereby decreases the rate of drainage. It also decreases the gas permeability of liquid lamella and as a result the rate of interbubble diffusion is retarded. A simple analysis incorporating both lamella drainage and interbubble diffusion has been developed. The qualitative predictions of this analysis are found to be consistent with our experimental observations.