In this study, a simple empirical decay function model is fitted to the experimental data to characterize the conformational changes of partially hydrolyzed polyacrylamide (HPAM) in semidilute solutions, using the stress recovery experiment after cessation of a steady shear flow processing. With the increase of HPAM concentration and NaCl concentration, the parameter K decreases, and this is in excellent agreement with the conformational changes of HPAM molecule chains. Experimental results show that the parameter K can provide some information on the changes of the polymer chain conformation. (c) 2006 Wiley Periodicals, Inc.