DNA was extracted from milk by collecting exfoliative cytology samples from dairy cows. A set of specific primers (α-La-F/R) was designed based on the α-Lactalbumin-encoding gene. A PCR method to detect milk allergens were established by screening the optimum experimental conditions. The results showed that the optimum PCR conditions were 56.5 ℃, 0.15 μmol/L and 35 for annealing temperature, primer concentration and number of cycles, respectively. The PCR method was highly specific and its sensitivity was 0.04 ng DNA. The PCR results of 10 types of commercial dairy products were identical to those described in the product label, suggesting this method to be accurate, reliable and thus applicable in practice.