MicroRNAs (miRNAs), an abundant class of highly conversed, small noncoding RNAs, present an entirely new way of post-transcriptional gene regulation. miRNAs play a key role in diverse biological processes, such as embryogenesis, differentiation, inflammation, viral infections, and carcinogenesis. Recently, more studies showed the importance of these noncoding small RNAs on immune system development and response, and miRNAs are found to involve in the regulation of immunity, including the development and differentiation of immnue cells, antibody production and the inflammatory mediator release. Here, the latest findings were summarized to explore the function and mechanism of miRNAs in modulating innate and adaptive immune responses.