The study Was carried out to determine the residue concentrations of peniccillin in Merket milk samples collected from some of the retail shops located in Seoul City. During the period from June to September 1974, 160 milk samples were collected and examined, using the Filter Paper Disk Method, for Screening test and Quantitative test of penicillin residue. The results obtained in the study were as follows: 1. Among the 160 Market Milk samples. 28 samples (17.5%) proved to contain some antibiotics residue. 2. In the case of the antibiotics residue positive milk samples, the rate of penicillin residue alone was 46.4% and the rate of the other antibiotics was 53.6%. 3. In the distribution of milk plants examined in relation-to the antibiotics residue positive milk samples, it was shown that S.K.H. and M.Market Milk plants had 15.0, 17.5, 20.0 and 17.5 percent respectively. 4. According to the monthly distribution, the highest antibiotics residue positive rate (25.0% of the samples) was shown in the samples collected in August, and the next (20.0% of the samples) in July. While the samples collected in June and September 1974 Showed lower rates of 7.5% and 17.5% respectively. 5. The range of the residue concentraction of penicillin in the positive milk samples were as follows: a. 53.8% of the total samples were found in the lowest range of 0.02-0.05 IU/ml. b. 30.8% of the total samples were found in the lower range of 0.05-0.1 IU/ml. c. 7.7% of the total samlpes were found in the higher range of 0.1-0.2 IU/ml. d. 7.7% of the total samples were found in the highest range of over 0.2 IU/ml.