Despite partial nephrectomy (PN) renal function preservation benefits, postoperative renal dysfunction may occur. Perirenal fat thickness (PFT) is associated with renal dysfunction such as diabetes; however, its role in renal tumour surgery is unclear. This study investigates the role of PFT in renal function after robot-assisted partial nephrectomy (RAPN). Pre-operative factors for postoperative renal dysfunction were analysed in 156 patients undergoing RAPN with ≥1-year follow-up. PFT measured using computed tomography categorised patients with PFT >21.0mm (median) as high-PFT. Tumour size, total R.E.N.A.L. nephrometry score and its N component, renal calyx opening, achievement of trifecta, and PFT were risk factors for renal dysfunction 1year postoperatively. Age ≥75years (p=0.024), total RNS ≥7 (p=0.036), and PFT >21.0mm (p=0.002) significantly correlated with postoperative renal dysfunction. CT-measured PFT is a valuable predictor of postoperative renal dysfunction.