Many recent studies have reported that microRNA (miRNA) biogenesis and function are related to the molecular mechanisms of various clinical diseases. Several methods, including northern blotting and DNA chip analyses, are capable of assessing miRNA-production patterns in cells. However, the development of repetitive monitoring of the miRNA-production profile in a noninvasive manner is demanded for the application of miRNAs to human medicine. Here, we describe a noninvasive system for monitoring miRNA biogenesis, from the stage of primary transcripts to that of mature miRNA regulation. We review the optical methods that have been developed to image miRNA production at each step of the miRNA-processing pathway in living subjects. We propose that an optical miRNA-imaging strategy, based on molecular imaging, can be used as an miRNA imaging detector to monitor various miRNAs, by using different reporters, simultaneously, for high-throughput screening, and will provide potential application for the diagnosis and therapeutics of multiple diseases.