Animal models are essential for biomedical research. Using them, the researchers are able to better understand the diseases, and search for more effective prophylactic and therapeutic approaches. Rodents are among the most frequently used species for scientific purposes. Chemical carcinogens’ administration is one of the most frequently used methods to establish animal models of cancer. Indeed, these chemicals have the ability to induce cancer development in several organs. The carcinogen N-methyl-N-nitrosourea (MNU) is the oldest member of the nitroso compounds with the ability to alkylate DNA. So, MNU is classified as a complete, potent, and direct alkylating agent. Depending on the animals' species and strain, dose, route, and age at the administration, MNU may induce cancer development in several organs, like breast, ovary, uterus, prostate, liver, spleen, kidney, stomach, small intestine, colon, hematopoietic system, lung, skin, retina, and urinary bladder. This work intended to review the experimental conditions to the chemical induction of cancer development in several organs with this carcinogen agent, with a special emphasis in the mammary carcinogenesis.