Coagulation/flocculation/sedimentation (CFS) pre-treatment was used to treat oil sands process-affected water (OSPW). The process was optimized in order to achieve a high removal of turbidity and total organic carbon (TOC). Aluminum sulfate (alum), ferric sulfate, and ferric chloride were used as the coagulants, and synthetic organic polymers (cationic, anionic, and nonionic) were also tested as the coagulant aids to increase the efficiency of the process. The addition of the alum resulted in a superior performance compared to that of ferric salts. Based on the turbidity and TOC removals, 250 mg/L of alum was chosen as the optimum condition, which resulted in the turbidity, TOC, and naphthenic acids (NAs) removal of 97-99%, 12-20% and 10-37%, respectively. The addition of 5 mg/L of cationic polymer to 250 mg alum/L during the coagulation slightly increased the TOC removal, but did not increase the NAs removal over alum treatment alone. The obtained result highlights the applicability of the CFS process to remove the dissolved NAs from OSPW. Zeta potential measurement indicated that the dominant removal mechanism at optimized condition was the destabilization of the particles through charge neutralization by adsorption of the aluminum hydroxide precipitates. Surface functional groups analysis also confirmed the removal of the particles and organic compounds, including NAs, by the growing flocs from OSPW.