One of the most important water treatment processes, is the coagulation suspended particle in the water by coagulants. Inorganic and polymers coagulants such as poly aluminum chloride and ferric chloride as a coagulant used mainely to remove turbidity of the water. These conventional coagulant have many problems in using such as changes in pH water, produce large volumes of sludge, residual heavy metals in water, and they could have potential probleme on human health. Many efforts have been done to replace conventional chemical coagulants with natural origin coagulants. The aim of this study was to evaluate the efficacy of two natural coagulant. These two natural coagulant are tannic acid and calcium lactate and they was compared with conventional coagulants poly aluminum chloride and ferric chloride respectively. Experiments was done by the jar test on the entrance raw water in the Isfahan water treatment plant. Factors that was studied include coagulant aid dosage, pH, turbidity and temperature. Experiment was designed by using the optimum design methods in order to evaluate the effect of factors and their interactions, as well as to optimize coagulation procedure conditions. Experiment result showed that in the optimal condition, calcium lactate able to reduce the turbidity to 0.36 NTU and the most important factor on the performance of calcium lactate is PH. The final turbidity in the optimal condition of tannic acid was 0.59 NTU and interaction of pH and the temperature was the most important factor in the performance of tannic acid. The final turbidity in the optimal condition of poly aluminum chloride was 0.56 NTU and second-order temperature is the most important factor on the performance of poly aluminum chloride. The final turbidity in the optimal condition of Ferric was 0.76 NTU and initial turbidity was the most important factor in the performance of Ferric Chloride. The results showed that natural coagulant have better performance and they able to reduce the turbidity below the standards levels .Comparison between the used materials showed thst the amount of sludge, the pH and alkalinity of water after coagulation and flocculation in a natural coagulant are less than the an inorganic coagulant. Also the amount of residual aluminum in water treatment with poly aluminum was measured 0.13 mg per liter tahat is higher than standard level. Finally, according to the compersion results of four coagulant and simple multi-criteria analysis, calcium lactate have better performance. Keywords : Calcium lactate, Coagulants, Ferric Chloride, Jar, Poly aluminum chloride, Response surface, Tannic acid.