Abstract: miRNAs, 18~23 nucleotide are a class of single stranded small non-coding RNA encoded by endogenous genes, which regulate gene expression at the post-transcriptional level. Abberant expressions of miRNAs reported in many kinds of human cancers may associate with cancer pathogenesis, tumor growth and metastasis, thus they can function as either oncogenes or antioncogenes. Numerous evidences indicated that the disregulation of miRNAs contribute to tumor initiation and progression. So these miRNAs can be used as clinical diagnosis biomarkers in many cancers, including non-small-cell lung cancer, breast cancer and prostate cancer. We introduce the clinical applications of the current known of miRNAs in early diagnosis, therapy and prognosis of non-small-cell lung
cancer, breast cancer and prostate cancer, as well as their molecular mechanisms.