A nano-silica dendrimer, poly(amidoamine)-grafted nanosilica (nano-PAMAM), catalyzed the Knoevenagel reaction of aryl and aliphatic aldehydes with various active methylene compounds at room temperature in good yields. The reaction conditions were mild enough that base-sensitive AcO or acid-sensitive THPO groups remained intact in the products. The catalyst was recycled up to 4 times in 78% average yield.