As part of the ecotoxicological tests on anuran tadpoles, the authors propose to study the sensitivity of different stages towards a nitrogenous compound frequently used in Morocco (Ammonium sulphate). For this purpose, the acute toxicity tests on tadpoles of two species (Bufo mauritanicus and Rana ridibunda) belonging to different stages of development were carried out. The lethal effects after 96 hours caused by the pollutant used as a reference (potassium dichromate) as well as ammonium sulfate increase with concentration and vary according to the stage of development. Significant differences were observed in the sensitivity of the tadpoles to pollutants according to the stage of development. The tadpoles belonging to the early stages of development (stage 24 according to Gosner, 1960) show greater acute effects on pollutants than the tadpoles belonging to the advanced stages of development (Stage 36 according to Gosner, 1960). After 96 hours, the lowest effective concentration (LOEC) is observed in the tadpoles belonging to the early stages of development (Stage 24 according to Gosner, 1960) in Rana ridibunda exposed just to the lowest concentration used (20 mg/l of ammonium sulphate). Therefore, ammonium sulfate may play a role in the local decline of amphibians.