By means of immobilizing the acidic homopolymer, poly(4-styrenesulfonyl(perfluorobutylsulfonyl)imide) (PSFSI), onto SBA-15 silica, anew type of strongly acidic composite catalyst was developed. The properties of the catalyst were characterized by NMR, FT-IR, XRD, SEM, TEM, XPS, TG, and CPC. The solid acid catalyst was highly effective and could be recycled at least five times without obvious loss of activity for the condensation of indole with structurally diverse aldehydes, which yielded diindolylmethane derivatives (DIMs). (C) 2009 Elsevier B.V. All rights reserved.