Abstract: During the years 2005 and 2006, samples of raw and of pasteurized milk (72 samples each) were collected randomly from various parts of Urmia city in Iran for the detection of aflatoxin M1. Aflatoxin M1 levels were assessed by Enzyme Linked Immuno Sorbent Assay (ELISA). There was a high incidence of AFM1 (100%), in both raw and pasteurized milk samples. The AFM1 levels in 6.25% of samples were higher than the maximum tolerance limit accepted by European Union (50 ng L-1), while the observed mean of AFM1 was lower than those proposed for European diets. Maximum level of AFM1 in raw and pasteurized samples were 91.8 and 28.5 ng L-1, while minimum levels were 4.3 and 5.1 ng L-1, respectively. The levels of AFM1 in total samples indicated that feeds for cows in this region were contaminated with AFB1 in such a level that appears to be a serious public health problem at the moment. Therefore, there is a need to limit exposure to aflatoxins by imposing regulatory limits.