MicroRNAs (miRNAs) are non-protein-coding small RNA molecules that negatively regulate target messenger RNA through degradation or suppression of protein translation. MiRNAs play important roles in the control of many biologic processes, such as development, differentiation, proliferation, and apoptosis. Increasing evidence shows that aberrant miRNA expression profiles and unique miRNA signaling pathways are present in a variety of cancers. MiRNAs function as oncogenes or tumor suppressors during tumor development and progression. Experimental evidence demonstrates that correction of specific miRNA alterations using miRNA mimics or antagomirs can normalize the gene regulatory network and signaling pathways, and reverse the phenotype in cancerous cells. MiRNA-based gene therapy provides an attractive anti-tumor approach for integrated cancer therapy. In this review, we focus on miRNA-based treatment for cancers, summarize the delivery systems used in experimental and preclinical research, such as liposomes, viral vectors, and nanoparticles, and consider the safety and toxicity of miRNA therapy.