Carry-over of the Aflatoxin M1 (AFM1) from contaminated milk to kefir and kefir grain and changes that occur during storage of kefir are investigated. Ultra high temperature (UHT) cow's milk purchased from a local market in Izmir and spiked to involve 0.1, 0.2 and 0.5 ppb AFM 1 in laboratory conditions was used in kefir production. AFM 1 contents of kefir and kefir grain were analysed by using combined immunoaffinity column clean-up and high performance liquid chromatography (HPLC) techniques. Carry-over ratio of AFM1 to kefir in respect to the 0.1, 0.2 and 0.5 ppb contamination levels were found to be 60, 60 and 80%, whereas the ratios in kefir grain were detected as 1.6, 2.6 and 2.6%. Results demonstrated that the carry-over of AFM1 from milk to kefir and kefir grain is higher at higher levels of the toxin. Storage of kefir at 4 ± 2°C did not influence the AFM1 content.