Polymer based on chitosan and tannin have been prepared and characterized using FTIR, UV, GC-Mass, X-ray spectra DSC and TG. All characterization techniques confirm the existence of chitosan and tannin. The effectiveness of chitosan-tannin polymer as a coagulant flocculant in treatment of surface water has been studied. Tests were carried out in laboratory on two kinds of water. The first one is synthesis water mixed with high and low concentrations of bentonite, simulating thus turbid water. The second one is raw water from the treatment station of Shatt Al-Arab River. The performance of coagulation flocculation process has been assessed by measuring the supernatant turbidity for different pH, doses and flocculation time of chitosan-tannin polymer. The obtained results show that chitosan-tannin polymer effectiveness was strongly dependent on pH and the doses of chitosan-tannin polymer, on the initial turbidity and on the water quality.