Sulfamic acid (H2NSO3H) has been used as an efficient and recyclable catalyst for acetalization and ketalization between carbonyl compounds and diols. This system is reasonably general and can be applied to converting several carbonyl compounds to the corresponding acetals and ketals using neopentyl glycol and other diols as protection reagents. The use of an inexpensive, green and stable catalyst, convenient reaction operation and high selectivity to desired products are the features contained in this reaction. Sulfamic acid can be reused five times in the reaction between benzaldehyde and neopentyl glycol without loss of activity. (c) 2005 Elsevier B.V. All rights reserved.