The green compression strength, mould permeability and hardness are the three important properties of the green sand mould. These mould properties are influenced by the sand type, sand grain size, grain shape, clay type, water content, ramming and mould wall thickness. The poor mould permeability and hardness value result in gas related casting defect and poor casting surface finish. Hence in this work, to predict the green sand mould permeability, the exponential models are developed for mould permeability, mould wall thickness and mould hardness value. The mould specimens of 50 mm diameter, 30/40//50/60/70 mm thickness with the hardness value of 87, 90 & 93 are prepared from the moulding sand. The permeability and hardness tests are carried out in the prepared specimens. Using these test results, graphs are plotted between the permeability and mould wall thickness for 87, 90 and 93 hardness values. The exponential model for each hardness value is developed to predict the permeability value for the different mould wall thicknesses.