In order to find the relationship between the frequency of sister chromatid exchange (SCE) in rats and polluted area a total of 36 specimens were captured from 15 localities in Korea and used for analysis of frequency of sister chromatid exchanges (SCEs), The results obtained were as follow. 1. The frequency of SCE per cell and per chromosome was 2.48±0.37 and 0.059±0.008, respectively. 2. The range of SCE number per cell was 0 to 7 with average 2.5 that was showed in 74.4% cells. 3. The SCE was occurred mainly in large chromosome groups belonging 1 to 10 at idiogram but very few SCEs were observed in X chromosome. 4. The range of SCE frequency according to the localities including polluted areas was 2.36±0.34 to 2.69±0.45 and showed no significant statistical difference. However, the specimens from Seoul showed relatively high SCE frequency (2.69±0.45) comparing with the average 2.48±0.37. This phenomena is believed that the environment in Seoul affect to the SCE. But, for the conclusion of this phenomeana more extensive sampling and intensive analysis are needed.