Purpose: We evaluated the effectiveness and safety of 18G biopsy gun with US guidence in the transplantedkidneys. Materials and methods: We performed 200 US-guided percutaneous biopsies using 18G biopsy gun. Diagnosticefficacy and complication of the biopsy in these patients were analyzed. Results: Biopsy specimens were adequatefor histologic diagnoses in 193 patients (96.5%). The mean of the biopsy frequency was 3, the mean of totalglomerular number was 21.64 and the mean glomerular number per one biopsy was 6.93. Major complications occured in3 (1.5%) of the 200 biopsies ; hematuria developed in two patients, AV fistula in one. These complications weresuccessfully controlled either by only transfusion or by coil embolization. There were no statistical differencein blood pressure, hemoglobin, BUN/Cr between pre- and post-renal biopsy. Conclusion: US-guided percutaneousbiopsy of renal allograft with 18G biopsy gun is simple, safe, and accurate method in evaluating the renalallograft dysfunction.