Following soda activation, the bentonite properties fluctuate and change more or less with time depending on the soda addition. Since these changes on activated bentonite properties are reflected in the further use of these products, controlling methods should be developed to optimize the product quality. In this study, optimization was achieved using the Response Surface Regression method (RSM) for activated calcium bentonites used in foundry sands. Evaluating the influence of soda addition and aging time on the bentonite properties, the activation conditions were optimized. (C) 2011 Elsevier B.V. All rights reserved.