Abstract:The microRNA (miRNA) is one of RNAs, with about 22 nucleotides, short and noncoding, that mainly regulates the gene expression at the postranscriptional level. According to the degree of base pairing to its complementary sites within its 3'-untranslated region (3'UTR), it degrades or negatively regulates the translation of the target miRNA. Mutation, deletion or over-expression of miRNA can cause physiological anomaly or disease and correlate with various human cancers. miRNAs involve tumor cell proliferation, differentiation and apoptosis processes in a role of oncogenes or tumor supressors. It is expected that microRNA might be applied in the diagnosis and treatment of malignant tumors as a powerful tool.