An amorphous silica-alumina catalyst with distinct bimodal pore structure was prepared by sol-gel reactions of tetraethoxysilane (TEOS) and aluminum nitrate in the presence of poly(ethylene oxide) (PEO). It contains macropores effective for rapid molecular transportation and mesopores providing a large specific surface area of similar to 600 m(2) g(-1). The pore size distribution of the macropores is sharp and its average diameter varies from 0.3 to 5 mum by altering the starting compositions such as water/TEOS and PEO/TEOS weight ratios. The macropores are formed when transitional morphologies of spinodal decomposition are fixed by sol-gel transition of inorganic components, and their size is controlled by altering the timing of the onset of spinodal decomposition and gelation. A change in the starting composition would affect this timing. In addition to macropores, silica-alumina has a large number of Bronsted acid sites, and shows excellent catalytic activity in the cracking of cumene. PEO would have the effect of increasing the uniformity of Al atoms in the silica network, which would be a cause of the formation of Bronsted acid sites.