PURPOSE: We evaluated the effectiveness and safety of 18G biopsy gun with US guidence in the transplanted kidneys. MATERIALS AND METHODS: We performed 200 US-guided percutaneous biopsies using 18G biopsy gun. Diagnostic efficacy and complication of the biopsy in these patients were analyzed. RESULTS: Biopsy specimens were adequate for histologic diagnoses in 193 patients(96.5%). The mean of the biopsy frequency was 3, the mean of total glomerular number was 21.64 and the mean glomerular number per one biopsy was 6.93. Major complications occured in 3 (1.5%) of the 200 biopsies; hematuria developed in two patients, AV fistula in one. These complications were successfully controlled either by only transfusion or by coil embolization. There were no statistical differences in blood pressure, hemoglobin, BUN/Cr between pre- and post-renal biopsies. CONCLUSION: US-guided percutaneous biopsy of renal allograft with 18G biopsy gun is simple, safe, and accurate method in evaluating the renal allograft dysfunction.