miRNAs are well-known as non-coding RNAs which regulate genes related to cancer progression. They can regulate their target genes, negatively and play a critical role as oncogenic and tumor-suppressive miRNAs. They can inhibit and promote cancer development through suppressing the expression of oncogenic and tumor-suppressive genes, respectively. This chapter introduces a number of dysregulated miRNAs participated in cell growth, apoptosis, migration, EMT, and angiogenesis of various types of cancers. Also, it presents the molecular mechanisms involved in deregulation of miRNAs in cancer. Finally, several therapeutic delivery systems of miRNAs are introduced in order to apply miRNAs as novel therapeutic strategies to treatment of cancers.