Objective To evaluate the efficacy of zero ischemia index (ZⅡ) in predicting the complexity and perioperative outcomes of off-clamp nephron-sparing surgery (NSS).Methods The patients between June 2016 and June 2017 in our institution who underwent off-clamp NSS were prospectively evaluated.ZⅡ was defined as the product of the tumor diameter and depth within renal parenchyma.The ZⅡ ＞6 defined as higher risk while ZⅡ ≤ 6 defined as low risk.The operating time,estimated blood loss,hospital stay,drainage,and complication rate were analyzed.Results There were 35 males and 10 females with average age of 42 y(range 23-76y).Mean tumor size was 2.4 cm (range 0.8-4.2 cm).Mini-flank approach open NSS was performed in 33 cases and laparoscopic NSS was performed in 12 cases.Off-clamp NSS was successfully performed in 44 patients except for renal artery occlusion in 1 case.Mean operative time was (95.0± 17.5) min (range 50-150 min);The average estimated blood loss was (152.4 ± 134.2) ml (range 20-600 ml);Mean postoperative drainage was (97.3 ± 59.7) ml (range 50-300 md);Mean postoperative hospital stay was (6.1 ± 1.3) d (range 5-8 d).Not severe post operative complication was observed.There were 37 patients in low risk group and 8 patients in high risk group.Operating time was significantly longer in high risk group [(118.8 ± 14.6 min) vs.(89.9±13.4) min,P＜0.01].EBL [(375.0±158.1) ml vs.(104.3 ±61.4) ml,P＜0.01] and drainage [(161.2±91.3)ml vs.(83.5 ±40.4)ml,P ＜ 0.01] were also significantly higher in high risk group.But there was no significant difference in hospital stay between two groups.The postoperative pathology indicated that 35 cases of clear cell carcinomas,2 cases of chromophobe renal cell carcinomas,one case of papillary carcinoma and seven cases of angiomyolipomas.Conclusions The ZⅡ is a novel and effective measurable criterion which can help predict the risk of perioperative outcomes of off-clamp NSS.ZⅡ =6 is established as a preliminary threshold for patient selection of off-clamp NSS.