The aggregation kinetics of silver nanoparticles (AgNPs) that were coated with two commonly use agentscitrate and polyvinylpyrrolidone (PVP)were investigated. Time-resolved dynamic light (DLS) was employed to measure the aggregation kinetics of the AgNPs over a range of monovalen electrolyte concentrations. The aggregation behavior of citrate-coated AgNPs in NaCl was in excel with the predictions based on DerjaguinLandauVerweyOverbeek (DLVO) theory, and the Ham of citrate-coated AgNPs in aqueous solutions was derived to be 3.7 × 10 J. Divalent electrolytes efficient in destabilizing the citrate-coated AgNPs, as indicated by the considerably lower critical c concentrations (2.1 mM CaCl and 2.7 mM MgCl vs. 47.6 mM NaCl). The PVP-coated AgNPs w significantly more stable than citrate-coated AgNPs in both NaCl and CaCl , which is likely due to repulsion imparted by the large, non-charged polymers. The addition of humic acid resulted in the the macromolecules on both citrate- and PVP-coated AgNPs. The adsorption of humic acid induce electrosteric repulsion that elevated the stability of both nanoparticles in suspensions containing Na concentrations of CaCl . Conversely, enhanced aggregation occurred for both nanoparticles at high concentrations due to interparticle bridging by humic acid clusters.