Between September 2006 and September 2007, 236 samples of raw (n=140), pasteurized (n=48) and UHT (n=48) milk were collected from supermarkets and from bulk milk tanks of eight dairy plants in the cities of Esfahan and Shahr-e Kord, Iran. All samples were analyzed for aflatoxin M 1 (AFM 1 ) contamination by ELISA and 213 (90.3%) were positive with mean concentrations 65 ng.l −1 . These concentrations are lower than the standards of Codex Alimentarius and FDA (500 ng.l −1 ), but 119 samples (55.9%) had higher concentrations than the maximum tolerance accepted by some European countries (50 ng.l −1 ). Mean concentrations of AFM 1 in raw, pasteurized and UHT milk were 68, 56, and 65 ng.l −1 , respectively. Mean concentrations of AFM 1 in autumn and winter samples were significantly higher (P<0.05) than those of spring and summer but differences between AFM 1 concentrations of spring and summer samples were not significantly different.Concentrations of AFM 1 in milk from Shahr-e Kord were significantly lower (P≤0.05) than those from Esfahan.