Aiming to determine the presence of aflatoxin M1 (AFM1) in milk, 84 samples were collected in different milk production units from Mexico State; in different seasons (dry and rainy). The analyte was determined by ELISA test, with the RIDASCREEN Aflatoxin M1® kit, results were expressed descriptively and compared with reference values. From the analyzed samples, 45% were positive. When establishing different concentration ranges, four samples were observed with a level of 0.001 <0.002; forty-two in the range of 0.003> 0.044; and, thirty-eight in the range of 0.50> 0.080. When obtaining 42 samples per season, 37 (0.075 ± 0.010 ppt) were positive for AFM1 in the period from August to February 2017, while from March to October 2018, only one sample was positive (with a level of 0.060 ppt). The AFM1 present in milk is a risk factor for consumers and livestock as well, therefore, measures in the production and storage of fodder and grains should be assessed before, during and after feeding the cattle.