The aim of this study was to determine the level of aflatoxin M 1 (AFM 1 ) in pasteurized and UHT milk marketed in Dar es Salaam, Tanzania. AFM 1 in pasteurized milk samples (75) and ultra-high temperature (UHT) milk (43) was determined by using immuno-affinity high performance liquid chromatography. AFM 1 was detected in 97% (115/118) of samples that consisted of 96% (72/75) of pasteurized milk samples and 100% (43/43) of UHT milk samples. About 82% of the contaminated pasteurized and UHT had AFM 1 levels above EU acceptable levels (0.05 µg/L). However, none of the contaminated pasteurized and UHT milk sample had levels of AFM 1 above the maximum recommended Codex limits (0.5 µg/L). The results indicate that the contamination of the samples with AFM 1 at such level could pose a serious public health problem. Thus, regular monitoring of AFM 1 levels in milk is important in order to protect consumers.