The purpose of this study was to evaluate the effect of renal artery embolization with small and narrowly calibrated microparticles on the coagulation diameter, volume, and shape of radiofrequency ablations (RFAs) in porcine kidneys. Forty-eight RFAs were performed in 24 kidneys of 12 pigs. In 6 animals, bilateral renal artery embolization was performed with small and narrowly calibrated microparticles. Upper and lower kidney poles were ablated with identical system parameters. Applying three-dimensional segmentation software, RFAs were segmented on registered 2 mm-thin macroscopic slices. Length, depth, width, volume_segmented, and volume_calculated were determined to describe the size of the RFAs. To evaluate the shape of the RFAs, depth-to-width ratio (perfect symmetry-to-lesion length was indicated by a ratio of 1), sphericity ratio (perfect sphere was indicated by a sphericity ratio of 1), eccentricity (perfect sphere was indicated by an eccentricity of 0), and circularity (perfect circle was indicated by a circularity of 1) were determined. Embolized compared with nonembolized RFAs showed significantly greater depth (23.4 ± 3.6 vs. 17.2 ± 1.8 mm; p < 0.001) and width (20.1 ± 2.9 vs. 12.6 ± 3.7 mm; p < 0.001); significantly larger volume_segmented (8.6 ± 3.2 vs. 3.0 ± 0.7 ml; p < 0.001) and volume_calculated (8.4 ± 3.0 ml vs. 3.3 ± 1.1 ml; p < 0.001); significantly lower depth-to-width (1.17 ± 0.10 vs. 1.48 ± 0.44; p < 0.05), sphericity (1.55 ± 0.44 vs. 1.96 ± 0.43; p < 0.01), and eccentricity (0.84 ± 0.61 vs. 1.73 ± 0.91; p < 0.01) ratios; and significantly greater circularity (0.62 ± 0.14 vs. 0.45 ± 0.16; p < 0.01). Renal artery embolization with small and narrowly calibrated microparticles affected the coagulation diameter, volume, and shape of RFAs in porcine kidneys. Embolized RFAs were significantly larger and more spherical compared with nonembolized RFAs.