Objective: To explore the outcome and surgical technique of minimally invasive unicompartmental knee arthroplasty (UKA) for spontaneous osteonecrosis of the knee. Methods: Twenty-seven patients with medial compartmental spontaneous osteonecrosis treated by minimally invasive Oxford phase 3 UKA from January 2009 to June 2013 were reviewed retrospectively. Twelve subjects were men and 15 women, with an average age of 64.6 +/- 8.6 years (52-82 years). At the time of diagnosis, 11 patients had with grade III necrosis and 16 grade IV according to Mont's classification. Pain, range of motion (ROM) and Hospital for Special Surgery (HSS) knee scores were evaluated before and after UKA. Pre-and postoperative alignment of the lower limbs was measured and compared. Postoperative radiographic assessments were made according to the guidelines proposed by the Oxford group at the final follow-up. Results: All patients were followed for a mean time of 27.8 +/- 15.9 months (6-59 months). There were no serious adverse events, such as infection, bearing dislocation, aseptic loosening, pulmonary embolism, deep venous thrombosis, cardio-cerebral vascular incident or psychological problems. One revision was required for unrelated causes (fracture of tibia plateau) 3 years after arthroplasty. One femoral component was tilted with a postoperative radiographic angle >10 degrees. One radiolucent line was observed in a patient with spontaneous osteonecrosis of the knee. The two patients with implant failure had no symptoms at last follow-up. Visual analogue scale scores decreased from 6.9 +/- 0.9 to 2.0 +/- 1.1 (t = 19.27, P = 0.00). Pain was relieved in 96.3% of subjects (26/27). The mean post-operative ROM and femorotibial angle were 125.7 degrees +/- 9.6 degrees and 177.7 degrees +/- 3.1 degrees, respectively. HSS scores increased from 61.3 +/- 9.7 to 93.0 +/- 4.8 (t = 14.46, P = 0.00). Of the 27 patients, 26 (96.3%) were satisfied with the outcome of this surgical procedure. Conclusion: Minimally invasive UKA is an effective means of managing spontaneous osteonecrosis of the knee. The short-term outcome of UKA is encouraging.