Cancer testis(CT)antigens have received particular attention in cancer immunotherapy.OY-TES-1 is a member of CT antigens.This study was to evaluate OY-TES-1 expression and immunogenicity in hepatocelluar carcinoma(HCC).OY-TES-1 mRNA expression was detected in 56 HCC tissues and 5 normal liver tissues by reverse transcriptase PCR(RT-PCR).Of the 56 cases of HCC tissues tested,37 cases had tumor and matched adjacent non-cancer tissues and were subjected to both RT-PCR and quantitative real-time PCR.OY-TES-1 protein was subsequently observed on a panel of tissue microarrays.Sera from patients were tested for OY-TES-1 antibody by ELISA.To identify OY-TES-1 capable of inducing cellular immune response,OY-TES-1 protein was used to sensitize dentritic cells and the cytotoxicity effect was measured in vitro.The results showed that OY-TES-1 mRNA was highly expressed in 41 of the 56(73.21％)HCC tissues,whereas none in 5 normal liver tissues.OY-TES-1 mRNA was frequently expressed not only in HCC tissues(72.97％,27/37),but also in paired adjacent non-cancer tissues(64.86％,24/37).But the mean expression level of OY-TES-1 mRNA in HCC tissues was significantly higher than that in adjacent non-cancer tissues(0.76854 vs.0.09834,P=0.021).Immunohistochemistry showed that OY-TES-1 protein expression was detected in 6 of the 49 cases of HCC tissues,and absent in 9 cases of normal liver and 6 cases of cirrhosis tissues.Seropositivity was detected in 10 of the 45 HCC patients,but not detected in 17 cirrhosis patients and 76 healthy donors.The specific cytotoxic T cells elicited by OY-TES-1 could kill HLA-A2+HCC cell line which expressed OY-TES-1.The target lysis was mainly HLA class I-dependent and could be blocked by antibodies against monomorphic HLA class I but not HLA classⅡ molecule.In summary,OY-TES-1 expression is up-regulated in HCC tissues and can be recognized by humoral and cellular responses,which suggests that OY-TES-1 is an attractive target for tumor immunotherapy in HCC.