Silica gel, as a heterogeneous catalyst has been applied for the highly selective C-S bond formation versus C-N and C-O ones via Michael addition of thiols to alpha,beta-unsaturated ketones under solvent-free conditions at 50 degrees C. The catalyst has been separated easily and reused in five runs without observable loss of its catalytic activity. (c) 2006 Published by Elsevier B.V.