Five clay Moroccan origins were employed during the coagulation-flocculation process which is evaluated in treatment of domestic wastewater on the basis of organic material as Chemical Oxygen Demand (COD) and Total Suspended Solids (TSS) removal efficiency. The influence of coagulant dosages and pH on the coagulation-flocculation efficiency process was studied and conditions were optimized corresponding to the best removal of COD and TSS. The optimum doses of each clay were 25 mg/l of perlite, 100 mg/l of clay of Safi and 200 mg/l of stevensite and two clays of Fes. The rate of COD removal was of 66.8%, 60.5%, 57.6%, 54.5% and 44.5% respectively of perlite, clay of Safi, clay of Fes1, stevensite and clay of Fes2. The influence of pH on coagulation effect was investigated under the optimum dosage. Results show that coagulants gave excellent COD and TSS removal efficiency when pH was 10. The clay of Safi has the lowest cost compared to other but perlite has been selected to avoid handling and storage of large volumes of clay at the treatment facility and particularly avoid high production of clayey sludge (to remove 1 kg of COD, we need 207 g of Sc while only 47 g of perlite are sufficient).