Adsorption of a low linear charge density cationic polyacrylamide (CPAM) onto monodisperse silica particles has been studied over a wide range of KCI concentration (10(-3)-1 M) and pH (4-9). In parallel the surface charge density of silica particles with and without adsorbed polyelectrolyte has been determined, The adsorbed amount (Gamma) as a function of electrolyte concentration (c(s)) exhibits a maximum at c(s) approximate to 0.1 M. As pH increases from 4 to 6, Gamma increases and then either reaches a plateau (c(s) less than or equal to 0.1 M) or decreases (c(s) > 0.1 M). These features can be rationalized in terms of the interplay between the different factors that govern polyelectrolyte adsorption. The effect of polyelectrolyte adsorption on the surface charge density of silica is largest at low c(s). It decreases with increase of the salt content and vanishes at c(s) > 0.1 M. This suggests that at electrolyte concentrations lower than 0.1 M, the polyelectrolyte plays a dominant in surface charge regulation, The ratio of the adsorbed polyelectrolyte charge to total surface charge is close to unity at high pH. It increases drastically with decreasing pH and increasing salt. A large overcompensation of the substrate charge by polyelectrolyte at these conditions is established in the present work.