Normal size of thyroid gland in Korean male and female were aimed to study through color scanning usingradioactive materials. The measurement of the size of thyroid gland is necessary not only for standardization ofKorean subjects but also to the dose determination of radioactive iodine treatment and evaluation of thyroiddisease. There had been no available data in regarding Korean euthyroid size in literature. In 119 subjects fromthe age of 19 years to 60 years, who have normal thyroid function and no history of any thyroid disorder, thelength, the width and the area of thyroid gland were measured in scan images. The weight of thyroid gland wascalculated by Allen-Goodwin's formula. The thyroid scan was obtained by Picker Color Magna-Scanner, in 24 hoursafter ingestion of 50 Ci sodium iodine I-131. Results: In males, 16 subjects among 119 cases, the mean values wereas following: length-5.1cm, width-2.5cm, area-9.1mm2, weight-14.7gr in right lobe, length-4.7cm, width- 2.3cm,area-7.6cm2, weight-11.1gr in left lobe, total area-16.7cm2, and total weight-25.8gr In females, 103 subjectsamong 119 cases, the mean values were as following: length-5.1cm, width-2.4cm, area-9.4cm2, weight-15.2gr in rightlobe, length-4.6cm, width-2.2cm, area-7.9cm2, weight-11.6gr in left lobe, total area-17.3cm2, total weight-26.8gr.The right lobe was larger in the above mean values of size than the left:11% longer in length, 8% wider in width, 18% broader in area and 30% heaview in weight in mean values. The difference of sizes between two lobes wasstatistically significant. There was no significant difference comparison with English written literature.