Abstract: To study the tissue distribution and metabolism of radioactivity in rats after single intravenous administration of ¹²⁵I-rAncrod（1.59 μg•kg^-1）. The concentration of ¹²⁵I-rAncrod in various tissue and body fluids were determined by ¹²⁵I labeled rAncrod combined with size exclusion chromatography （SEC） and γ-counting methods. The concentration of ¹²⁵I-rAncrod predominantly accumulated in the thyroid and gastrointestinal and also be found in the kidney and liver in fair amounts, but in brain, spinal cord, muscle and fat was at a very low level. After single intravenous administration (chemical dose 1.59 μg•kg^-1) of ¹²⁵I-rAncrod to Wistar rats, the samples of feces, urine and bile were analyzed by SEC. The result was that parent drug was not existed in feces, urine and bile in 48 h. The results showed that ¹²⁵I-rAncrod was distributed widely in rats, metabolic process was complete.