The present invention provides RNAs for efficiently inhibiting miRNAs, vectors for expressing the RNAs in cells, methods for constructing the vectors, methods for inhibiting miRNAs using the RNAs, and such. It was discovered that a miRNA-inhibiting RNA complex comprising a double-stranded structure, wherein at least one RNA strand comprising a miRNA-binding sequence is linked to the two strands at at least one end of the double-stranded structure, can efficiently inhibit miRNAs. In particular, RNAs in which two RNAs containing a miRNA binding sequence are positioned between two double-stranded structures were able to strongly inhibit miRNA. These RNAs can be expressed from, for example, a PolIII promoter, and by integration into a retroviral vector, miRNAs can be stably inhibited for a long period of time. The present invention provides tools that are useful for regulating miRNAs. Their use is expected for gene regulation, gene therapy, and such in differentiation, tumorigenesis, development, infection, and such wherein miRNAs are involved.
