Tin(IV) ion-exchanged montmorillonite (Sn-Mont) was found to be an excellent solid acid catalyst for the Mukaiyama aldol reactions of congested ketones with silicon enolates from ketones as well as esters. It was disclosed that Sn-Mont was far more active than other metal ion- or proton-exchanged montmorillonites and typical homogeneous acid catalysts such as TMSOTf and BF3 center dot OEt2.