Abstract: Determination of the carrier content in ~(125)I solution by ion-selective electrodes has been investigated. The stability of ion-selective electro- des in 24 hours is less than 1 mⅤ. The reproducibility is 0.7％.The slope of the calibration curve is 95％—99％ of the theoretical value. The concentration range of determination is 0.3μg/ml—10mg/ml.The limit of detection is (3—5)×10~(-2)μg/ml. The determinable pH range is 2—13. Comparing with spectrophotometry, the analytical results agree. The range of determination is wide. The method is simple, easy and fast. The radiation dose is abated. The method is currently used in routine quality-control.