Salinity effect on retardation efficiency of ammonium chloride (NH4Cl) on the polyacrylamide (PAM) that influences the gelation time of PAM-based polymer gel is an interesting phenomenon. This paper presents a concise investigation of molecular interaction of PAM with NH4Cl in high salinity conditions. This study quantified the ionic bonding of carboxylate group of PAM with ammonium ion of NH4Cl. Zeta potential and hydrodynamic radius of the prepared polymer solutions were measured using zeta potential analyzer and dynamic light scattering (DLS) technology, respectively. High salinity is represented in high concentration of sodium chloride (NaCl). From the experimental results, it shows that without NaCl and NH4Cl, the whole absolute value number of the zeta potential of polyacrylamide seems to increase linearly, while the hydrodynamic radius shows a significant increase. In addition, zeta potential and hydrodynamic radius of PAM decreases with salinity. The absolute value of zeta potential reduces with the concentration of NH4Cl as retarder. On the other hand, the hydrodynamic radius tends to increase with NH4Cl retarder. It may be because of tighter bonding of NH4+ ions with carboxylate groups of polymer. The zeta potential and hydrodynamic radius are fairly affected by the exposure time of polymer to high temperature. Higher salinity reduces the effectiveness of polymer to stretch and it in turns decreases the zeta potential and hydrodynamic radius. © 2019 Author(s).