Toxic heavy metals and especially lead (Pb), cadmium (Cd) and mercury (Hg) can easily transmit to humans through consumption of contaminated milk. The present research was done to study the concentrations of Pb, Cd and Hg in different types of milk samples. In total, 1100 bovine, ovine, caprine, buffalo and camel raw milk samples were collected in different regions of Iran and analyzed to determine concentrations of Pb, Cd and Hg by a graphite furnace atomic absorption spectrometric method. The mean recoveries of the analytical method were 88%, 93%, and 96%, for Hg, Cd and Pb, respectively. The mean Cd, Pb and Hg contents obtained from 1100 samples were 3.62±0.35 ppb (range: 0.06-14.03 ppb), 11.73±1.09 ppb (range: 0.12-33.62 ppb) and 4.35±0.42 ppb (range: 1.03-10.38 ppb), respectively. The highest concentrations of Cd, Pb and Hg were found in raw bovine samples (4.05±0.38, 12.36±1.21 and 5.76±0.53 ppb, respectively), while raw camel milk harbored the lowest concentrations of heavy metals. Milk of 5≤ year-old animals had the highest concentrations of Cd, Pb and Hg. Milk samples of all studied animals collected in spring had the highest concentrations of Cd, Pb and Hg heavy metals (P<0.05). The mean concentrations of Cd and Hg heavy metals were lower than the allowed limits announced by the standard organizations, while those of Pb were higher. These results highlight the importance of periodically monitoring levels of Cd, Pb and Hg heavy metals in milk of bovine, ovine, caprine, buffalo and camel – especially in spring and summer seasons and also in 5≤ year-old animals in Iran.