Objective: To examine the clinical effect of auxiliary liver transplantation with ultra-small volume graft in the treatment of portal hypertension. Methods: Twelve cases of portal hypertension treated by auxiliary liver transplantation with small volume graft at Liver Transplantation Center,Beijing Friendship Hospital, Capital Medical University between December 2014 and March 2022 were studied retrospectively. There were 8 males and 4 females,aged 14 to 66 years. Model for end-stage liver disease scores were 1 to 15 points and Child scores were 6 to 11 points. The grafts was derived from living donors in 9 cases,from split cadaveric donors in 2 cases,from whole cadaveric liver of child in 1 case. The graft recipient body weight ratios of 3 cadaveric donor livers were 0.79% to 0.90%, and of 9 living donor livers were 0.31% to 0.55%.In these cases, ultra-small volume grafts were implanted. The survivals of patient and graft, complications, portal vein blood flow of residual liver and graft, abdominal drainage and biochemical indexes of liver function were observed. Results: All the grafts and patients survived. Complications included outflow tract torsion in 2 cases, acute rejection in 1 case, bile leakage in 1 case, and thyroid cancer at the later stage of follow-up in 1 case, all of which were cured. The torsion of outflow tract was attributed to the change of anastomotic angle after the growth of donor liver. After the improvement of anastomotic method, the complication did not recur in the later stage. There was no complication of portal hypertension. The measurement of ultrasonic portal vein blood flow velocity showed that the blood flow of residual liver decreased significantly in the early stage after operation, and maintained a very low blood flow velocity or occlusion in the long term after operation, and the blood flow of transplanted liver was stable. Conclusions: Auxiliary liver transplantation can implant ultra-small donor liver through compensation of residual liver. This method may promote the development of living donor left lobe donation and split liver transplantation. However, the auxiliary liver transplantation is complex, and it is difficult to control the complications. Therefore, this method is currently limited to centers that are skilled in living related liver transplantation and that have complete ability to monitor and deal with complications.