A simple synthesis of microporous and micro/meso bimodal porous (NH4)(3)PW12O40 by reaction of in-situ generated [PW12O40](3-) with NH4+ in a strongly acidic solution is presented. Keggin-type phosphotungstate, [PW12O40](3-), was generated by a reaction of ammonium metatungstate, (NH4)(6)H2W12O40, and phosphoric acid, and the generated [PW12O40](3-) was spontaneously precipitated by a reaction with existing NH4+. The obtained (NH4)(3)PW12O40 had larger microporous volume and surface area than those of (NH4)(3)PW12O40 materials prepared by a common neutralization method (H3PW12O40 + 3(NH4)H-CO3 -> (NH4)(3)PW12O40 + 3H(2)O + 3CO(2)). By changing the P/W ratio in reaction media, not only microporous but also micro/meso bimodal porous (NH4)(3)PW12O40 could be prepared. The obtained (NH4)(3)PW12O40 showed heterogeneous catalytic activity for hydrolysis of ethyl acetate. (c) 2013 Elsevier Ltd. All rights reserved.