Samarium-exchanged heteropoly tungstate (SmxTPA) is an efficient catalyst for the synthesis of glycerol carbonate from glycerol and urea. The catalysts with varying Sm content were prepared and characterized by FT-IR spectroscopy, XRD, laser Raman spectroscopy, temperature-programmed desorption of ammonia, and X-ray photo electron spectroscopy. The activity of the catalysts is related to the Lewis and Brønsted acidity, which depends on the Sm content in the catalysts. Partially exchanged SmxTPA catalyst showed high activity, owing to a higher number of Lewis acidic sites. The catalyst exhibited consistent activity and selectivity during recycling. A plausible reaction mechanism is presented. The catalyst also exhibited high activity in the acid-catalyzed benzylation of anisole.