We proposed to undertake an experimental study on the combined toxicity of Lead and Cadmium in aquatic environment, for describing well the danger which run the alive beings which live there and on which the life depends on it. To achieve our goal, we used as biological material Gambusia affinis, a species sensitive to toxicity in order to check if the combined effects of heavy metals in fact Plomb and Cadmium would be the cause of disturbance in aquatic environment. We proceeded to test each salt individually and to determine the CL50 of them;then, to prepare a solution combined with the concentrations corresponding to the value of ½ CL50 of these two salts tested according to méthode(5). Taking into consideration these results obtained, the constant following is released:The Cadmium tested with the concentration of 0,1 G and its dilutions, is very toxic with a CL50 around 0,003 Mg that the solutions of Lead to the same concentration with a CL50 around 0,006 Mg. The biological tests of laboratory made it possible to prove the toxicity of each salt separately and to confirm the combined toxicity of these two heavy metals, owing to the fact that the combination of their ½ CL50 gives synergistic effects to the populations of Gambusia affinis. This study will precisely allow the scientific community, to the industrialists, and the government to manage our environment well, in order to especially avoid the danger due to the pollution with heavy metals which constitutes today a plague threatening the species of the aquatic environment, water, and the life of the human beings in general, in the mine fields of the DRC being a significant mining country.