PURPOSE: To compare the ablation zone after radiofrequency ablation (RFA) with saturated saline preinjection and renal artery occlusion in canine kidneys. MATERIALS AND METHODS: RFA was induced in the kidneys of six mongrel dogs. A total of 24 ablation zones were induced using a 1-cm tip internally cooled needle electrode in three groups: RFA (Control group), RFA with 0.5 mL saturated saline preinjection (SS group), and RFA with renal artery occlusion by atraumatic vascular clamp (Occlusion group). Ablation zone diameters were measured along transverse and longitudinal sections of the needle axis, and volumes were calculated. Temperature, applied voltage, current, and impedance during RFA were recorded automatically. RESULTS: The RFA zone volume was the largest in the SS group (1.33 +/- 0.34 cm3), followed by the Occlusion group (1.07 +/- 0.38 cm3) and then the Control group (0.62 +/- 0.09 cm3). Volumes for the SS and Occlusion groups were significantly larger than those for the Control group (p = 0.001, p = 0.012). There was no significant difference in volumes between the SS and Occlusion groups (p = 0.178). CONCLUSION: Saturated saline preinjection is as effective as renal arterial occlusion for expanding the ablation zone. RFA with saturated saline preinjection could help to treat large renal tumors.