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Considering the existence and amount of aflatoxin M1 in bulk cow’s milk in Tehran area, the reconstituted milk was contaminated with 2ppb aflatoxin M1 and the effect of lactoperoxidase system ‘ LPS “(Lactoperoxidase enzyme with two different concentration, 10 and 3oppm, thiocyanate 0.25Mm, hydrogen peroxide 0.25 Mm) and LPS plus riboflavin (0.25Mm) on degradation of aflatoxin M1 level were studied. In this study, the level of LPS system. was the same as its indigenous level in milk. The experimental samples (4 groups with 15 samples for each group) and control (One group with 15 samples) classified into three separate groups varied in temperature, and holding time. In trials 1, 2, 3 all of the control and experimental groups were incubated in 4°C for 12h, 4°C for 24h and 65°C for 3Omin respectively and finally afilatoxin M1 level was measured by TLC-Scanner. Regarding to the results of this study, M1 reduction in control groups 1, 2, 3 was 2.84%, 2.78% and 3.14% respectively. The mean rate of toxin reduction by lactoperoxidase system (LPS1O) in trials 1, 2, 3 was 51.800, 54.020 and 57.0820% respectively. Whenever enzyme concentration was increased three times in the system, the rate of toxin reduction was slightly increased in away that rates of aflatoxin M1 reduction in trials 1, 2, 3 was 52.680%, 57.460% and 67.460%. Lactoperoxidase system (LPS1O) plus riboflavin had more effectiveness on the aflatoxin M1 reduction in comparison with other substances, so that the rates of aflatoxin M1 reduction by this system and riboflavin in trials 1, 2, 3 was 91.600%, 93. 760% and 94.460%. LPS 30 in which enzyme concentration was 3U/ml milk plus riboflavin caused reduction of aflatoxin M1 in trials 1, 2, 3 in the rates of 94.420%, 94.240% and 98.320%. In general, level of aflatoxin M1 is significantly (P<0.05) reduced by lactoperoxidase system and riboflavin.