Three kinds of hydrophobically modified copolymers of acrylamide with 3-acrylamido-2-hydroxypropyltrialkylammonium chloride were prepared, in which alkyls were ethyl, butyl and octyl, respectively. The conformations of the hydrophobically modified copolymers were studied using TEM micrograph. The flocculation performances and the dewatering efficiencies were investigated. The results showed that the hydrophobic group could enhance the flocculation properties. The longer the hydrophobic alkyl chain was, the better the flocculation result was. Compared with poly-diallyldimethyl ammonium chloride (PDADMAC) and poly-acrylamide (PAM), the hydrophobically modified polymers showed better performances in turbidity removal and were quite more efficient in dewatering examination. (c) 2007 Published by Elsevier Ltd.