Objective To investigate the expression profile of microRNA-21 in human cholangiocarcinoma tissues and to validate its bona fide targets in human cholangiocarcinoma cells. Methods The expression profile of microRNA-21 in human cholangiocarcinoma tissues and cholangiocarcinoma cell line, QBC939, was evaluated by using real-time PCR analysis. The bona fide targets of microRNA-21 were analyzed and confirmed by dual luciferase reporter gene assay and western blot, respectively. The expressional correlation of microRNA-21 and its targets was probed in human cholangiocarcinoma tissues by using real-time PCR, locked nucleic acid in situ hybridization (LNA-ISH), and immunohistochemistry analysis. Results Real-time PCR analysis revealed that microRNA-21 expression depicted a significant up-regulation in human cholangiocarcinoma tissues about 5.6-fold as compared to the matched normal bileduct tissues (P<0.05). The dual luciferase reporter gene assay revealed endogenous microRNA-21 in cholangiocarcinoma cell line, QBC939, inhibited the luciferase reporter activities of wild-type PTEN (P<0.01) and PDCD4 (P<0.05) and had no this effect on mutated PTEN and PDCD4. Moreover, loss of microRNA-21 function led to a significant increase of PTEN and PDCD4 protein levels in QBC939 cells. Elevated microRNA-21 levels were accompanied by marked reductions of PTEN and PDCD4 expression in the same cholangiocarcinoma tissue. Conclusion microRNA-21 expression is up-regulated in human cholangiocarcinoma and PTEN, PDCD4 are direct effectors of microRNA-21. Objective To investigate the expression profile of microRNA-21 in human cholangiocarcinoma tissues and to validate its bona fide targets in human cholangiocarcinoma cells. Methods The expression profile of microRNA-21 in human cholangiocarcinoma tissues and cholangiocarcinoma cell line, QBC939, was evaluated by using real The bona fide targets of microRNA-21 were analyzed and confirmed by dual luciferase reporter gene assay and western blot, respectively. The expressional correlation of microRNA-21 and its targets was probed in human cholangiocarcinoma tissues by using real-time PCR, locked nucleic acid in situ hybridization (LNA-ISH), and immunohistochemistry analysis. Results Real-time PCR analysis revealed that microRNA-21 expression depicted a significant up-regulation in human cholangiocarcinoma tissues about 5.6-fold as compared to the matched normal bileduct tissues (P <0.05). The dual luciferase reporter gene assay revealed endogenous microRNA-21 in cholangioc arcinoma cell line, QBC939, inhibited the luciferase reporter activities of wild-type PTEN (P <0.01) and PDCD4 (P <0.05) and had no this effect on mutated PTEN and PDCD4. significant increase of PTEN and PDCD4 protein levels in QBC939 cells. Elevated microRNA-21 levels were accompanied by marked reductions of PTEN and PDCD4 expression in the same cholangiocarcinoma tissue. Conclusion microRNA-21 expression is up-regulated in human cholangiocarcinoma and PTEN, PDCD4 are direct effectors of microRNA-21.