Objective To investigate the value of Cylex ImmuKnow immune cell function assay in the diagnosis of infection after liver transplantation. Methods The objects of this prospective study were 48 patients undergoing orthotopic liver transplantation (OLT) in Liver Transplantation Center, the Third Affiliated Hospital of Sun Yat-sen University from July 2010 to December 2012. The informed consents of all patients were obtained and the ethical committee approval was received. According to whether the patients suffered clinical infection or not after OLT, they were divided into two groups:infection group (n=14) and non-infection group (n=34). Another 20 healthy people were enrolled as the control group. There were 11 males and 3 females in the infection group with a mean age of (47±10) years old. There were 29 males and 5 females in the non-infection group with a mean age of (45±9) years old. There were 10 males and 10 females in the control group with a mean age of (42±10) years old. Peripheral venous blood 2 ml was collected from the patients on the 7th day after OLT or from the healthy people when enrolled in control group. The adenosine triphosphate (ATP) level in cluster of differentiation (CD) 4+ lymphocyte was detected using Cylex ImmuKnow kit and the testing data were compared using t test. Results The ATP level in CD4+ cells was (178±58), (345±62), (467±84) mg/L in infection group, non-infection group and control group respectively. The ATP level in infection group was significantly lower than that in non-infection group (t =-4.6, P<0.05). The sensitivity of the Cylex ImmuKnow immune cell function assay in the diagnosis of infection after OLT was 0.79, the specificity was 0.85, the positive predictive value was 0.69, and the negative predictive value was 0.91. Conclusions Cylex ImmuKnow immune cell function assay can simply and quickly detect the immune cell function. It plays a role in monitoring and diagnosing the infection after OLT.