A newly prepared catalyst consisting of acidic ionic liquid 1-(4-sulfonic acid)butylpyridinium hydrogen sulfate supported on silica was used to catalyze the cross-aldol condensation of ketones with aromatic aldehydes under solvent-free conditions. The highly active and selective catalyst gave good to excellent yields of the desired cross-aldol products without the occurrence of any self-condensation reactions. Reaction times were short, the procedure and work-up were simple, and no volatile or hazardous organic solvents were necessary. Moreover, the catalyst could be reused at least four times with only a slight reduction in activity.