Heteropolyacids supported on activated carbon have been shown to be efficient solid catalysts for the esterification of acrylic acid by butanol in liquid phase. The reaction was carried out under batch and flow conditions and it was shown that such supported heteropolyacids display a better activity per proton than do conventional catalysts such as sulfuric acid or resins. It was also proved that under flow conditions deactivation of the catalyst was low (from 43 to 32% conversion) and was due to the dissolution of the supported heteropolyacid in the reaction medium (ca. 25% in the present case), after which a steady state stable catalyst was obtained, which makes such a system of prospective interest. In contrast, under batch conditions both polyanion dissolution and deposition of polymeric species resulted in deactivation of the catalyst (even in the presence of a polymerization inhibitor) which makes such a system not really reliable.