Mikro-RNAs are functional, non-protein coding RNA molecules and their transcriptions provided by intron or exon regions of the genome and non-protein coding regions of RNA genes. Mikro-RNAs inhibit translation of protein and / or cause destruction of mRNA. Most of studies have demonstrated that many of these small molecules have critical importance in many important cellular events such as hematopoiesis, differentiation, proliferation and apoptosis. The role of mikro-RNAs in malign diseases have become the subject of research increasingly. Mikro-RNAs play a role in different events such as cell growth, differentiation, proliferation and death by suppressing one or more target gene. More than 50% of miRNA genes are located on the genome which has associated with cancer. A large number of experimental studies show that miRNAs may have generate a new class of oncogenes or tumor suppressor gene. MiRNAs are thought to be identified at a different level of expression in normal and pathological tissues can be determined between the miRNAs that are effective diagnosis and treatment of human cancers.