The influence of the concentration of magnesium oxide and phosphoric acid on the removal of NH4+ present in the waters of the tannery dewatering process was studied in the following research work, using different concentrations of MgO / H3PO4. Previously the sample of water dislodged was joined a process of coagulation-flocculation, the coagulants that were used: aluminum polychloride (PAC) and aluminum chloride hexahydrate (AlCl3.6H2O); And polyacrylamide at 5ppm as a flocculant. The most efficient coagulant is PAC, with removal of 96% dissolved solids and 32% suspended solids. Also, the PAC at a concentration of 1200 ppm. Removes NH4+ from the system up to 10% The results show that the optimum NH4+ removal ratio is 1 / 1.2 (Mg2 + / PO43-), obtaining 39% in a first stage and 77% NH4+ removal in the second stage