Condensation of formaldehyde and methyl formate to methyl glycolate and methyl methoxy acetate catalyzed by 12-tungstosilicic compounds has been studied. Thermal pre-treatment of 12-tungstosilicic acid has a great influence on the activity of the acid. The most preferable pre-treatment temperature is 300 degrees C in the range of 100-350 degrees C. Water has a disadvantageous effect an the condensation reaction. 12-tungstosilicic acid and its acidic salts show high activity to the reaction, but the neutral salts have little activity. The influence of acid strength has also been investigated. (C) 2000 Elsevier Science B.V. All rights reserved.