The potential of supported heteropoly acids (HPAs) is of great significance in acid catalysis. In this contribution, the HPA H3PW12O40 (PW) was impregnated into SiMCM-41 and the resulting PW/SiMCM-41 acidic system was investigated by means of spectroscopy (MAS NMR, FTIR) and catalytic testing. The complexation of PW with the SiMCM-41 hydroxyls is purported to enhance the acidity and catalytic activity of these silanols.:The effect of PW loading on structure, acidity and catalytic performance is monitored. The host material suffers severe structural distortions at higher loadings which lead to a considerable loss in the structural order. Based on these experimental findings, both acidity and catalytic performance were optimal with a loading of around 23 wt.% PW.