Methoxyacetophenones were synthesized through Friedel-Crafts acylation of anisole with acetic anhydride using a silica-supported heteropolyphosphotungstic acid (HPW) catalyst. High conversions and very high p-selectivity were attained in the temperature range of 61-110degreesC. Nevertheless, the catalyst seemed to deactivate after half an hour at 61 and 83 degreesC, mainly due to strong but reversible adsorption of products. Cleaning the spent catalyst recovered the activity, indicating that it was stable under the experimental conditions and that the active HPW was not fairly leached from the silica support. In spite of this, the slower but progressive coking deactivated the catalyst. (C) 2003 Elsevier B.V. All rights reserved.