Objective To evaluate the effect and feasibility of mini-flank approach for open partial nephrectomy (MI-OPN) in complex renal tumors with high Zhongshan Score (ZS Score ≥8).Methods Between January 2012 and December 2014, the data from 25 patients with renal tumors , including 18 male and 7 female patients, were retrospectively reviewed.The average age was 50.2 years(range 26-75 years) and the average body mass index was 24.5 kg/m2(range 21.3-30.1 kg/m2).The initial symptom included asymptom in 17 cases, hematuria in 6 cases and other presentation in 2 cases.Bilateral renal tumors were found in 4 cases.Fifteen cases suffered with contralateral urinary stone , renal cyst or hydronephrosis .The preoperative serum creatinine level was 76.9 μmol/L ( range 47 -132 μmol/L ) and the preoperative estimated glomerular filtration rate (eGFR) was 103.8 ml/(min· 1.73 m2)(range 36.5-173.9).The ZS Score was 8 in 11 cases, 9 in 3 cases, 10 in 5 cases, 11 in 2 cases, 12 in 2 cases, and 13 in 2 cases.Mean maximum tumor size was 4.9 cm ( range 2.5-8.1 cm) in CT scan.The average length of incision was 8.0 cm( 7.5 -10.0 cm ) .During the operation , the mass and around normal renal tissue were exposed after opening the Gerota fascia.Along the dorsal of kidney , the renal artery was dissected and clamped .Then, the mass was completely removed along margin of 0.5-1.0 cm normal renal tissue.The vascular end was closed by 3-0 absorbable suture.The entire wound of kidney was U shaped closed by 2-0 absorbable suture.The operative time, ischemia time, estimate blood loss, pathology parameters, operative and short-term (2 -3 months) postoperative complications were recorded .Renal function was recorded 2 -3 months after operation.Results MI-OPN was successfully performed in 23 cases.Radical nephrectomy was performed in 1 cases due to the tumor invasion into the renal pelvis and ureteropelvic junction .Another radical nephrectomy was performed for suspection of positive margin .Mean operative time was 100.2 min ( range 75-150 min) , mean warm ischemia time was 28.3 min( range 21-39 min) and mean estimated blood loss was 63.6 ml(range 10-400 ml).Only 1 case accepted blood transfusion.Mean postoperative hospital stay was 6.6 days (range 5-9 days).Postoperative complications were found in 1 patient, who was found the fluid in surgical region and relieved after the drainage . The pathological diagnosis included clear cell carcinoma in 21 cases, papillary carcinoma in 3 cases and chromophobe cell tumor in 1 case.The mean postoperative serum creatinine level was 88.9μmol/L( range 61-189μmol/L) and the mean postoperative eGFR was 86.3 ml/( min· 1.73 m2 ) ( range 34.0-149.6 ) .There was significant difference between pre and postoperative renal function ( P<0.01 ) .During the average follow-up period of 13.7 months ( range 6-24 months ) , no local recurrence or metastasis occurred .Conclusion MI-OPN is an innovation of traditional OPN and suitable for the complex renal tumors with high ZS score .