As a new disease therapy method, gene therapy shows a broad application prospect. However, there are still lots of problems in gene therapy to be solved. To evaluate the efficiency of gene therapy, it is requisite to monitor and evaluate the localization and expression of the therapeutic gene in vivo. Radionuclide reporter gene imaging, with rapid development in recent years, is considered as a non-invasive and sensitive method in monitoring the expression of the therapeutic gene in vivo. This method, which has the advantage of high sensitivity and specificity and may carry on deep-tissue imaging and repeat imaging, has shown a good application prospect. The mechanism, characteristics and value of radionuclide reporter gene imaging in monitoring gene therapy are reviewed in this paper.