The structure and reactivity of silica-supported 12-tungstophosphoric acid (HPW) with 10-60 wt.% loading prepared by the impregnation method are studied by using chemical analysis, X-ray diffraction (XRD), FT-IR, FT-Raman, TG, P-31 MAS NMR, surface area measurement and microreactor tests. It is found that most of HPW in samples is well dispersed on the support, and may mainly exist as small crystalline particles with an average size around 24.3-27.6 nm, calculated by XRD results. Based on various characterization techniques, it may be concluded that silica-supported HPW still keeps its Keggin structure. The effect of different loading on the reactivity of silica-supported HPW without promoter or promoted by Pt/Al2O3 is studied by using isomerization of n-hexane as a probe reaction, and the reactivity is found to be strongly loading related. (C) 2003 Elsevier B.V. All rights reserved.