RNA interference has emerged as one of the most promising gene silencing techniques in gene function and gene therapy researches. However, the in- vivo application of small interference RNA (siRNA) requires an effective noninvasive method to evaluate its delivery in vivo. Nuclear imaging, luciferase imaging and bioluminescence imaging have potential values in this area. Applied widely in clinic and research, nuclear imaging has the advantages of noninvasiveness, high sensitivity and good safety, and it can be used in the large animal, even the human body. Moreover, nuclear imaging provides the information of biodistribution and semi-quantitative or quantitative evaluation in gene interference. The recent progress in in-vivo application basis, protection, radiolabeling methods, biodistribution, and nuclear imaging of siRNA is reviewed here, in order to help the development of siRNA based imaging and therapy researches.