A magnetically recoverable acid nanocatalyst, heteropolyacids/chitosan/Fe3O4 (HSiW-CS-Fe3O4), was successfully prepared by a one-pot synthesis method. The characterized results by XRD, TEM, TGA, FTIR and magnetic measurements testified that Keggin-type 12-silicotungstic acid (HSiW) was efficiently immobilized into the cross-linked chitosan (CS) coating on nanometer-sized Fe3O4 magnetic cores. The prepared HSiW-CS-Fe3O4 possesses a typical superparamagnetic behavior and has the acid capacity of 0.13 mmol/g. It exhibits higher catalytic activity in the acetalization reaction of benzaldehyde with ethylene glycol, and gives a 99% yield for acetal under mild reaction conditions. Furthermore, the prepared catalysts can be magnetically separated from the reaction system and reused 5 times without the significant loss of catalytic activities. It is also confirmed that the recovered catalysts are not dramatically changed in the physicochemical features. The prepared HSiW-CS-Fe3O4 may be the promising catalytic material in a mass production of the fine chemicals. (C) 2012 Elsevier B.V. All rights reserved.