Reactive oxygen species (ROS) are a cluster of highly reactive and short-lived oxygen-containing molecules that lead to metabolic disorders where production exceeds catabolism in an organism. Many specific radiotracers for positron/single-photon emission tomography have been developed to reveal the discrepancy of ROS levels in normal and damaged tissues and further clarify the relationship between ROS and diseases. This review summarizes the advances achieved for the development of ROS radiotracers to date. The structure design, radiosynthesis, and imaging performance of existing radiotracers are discussed with the individual ROS-response mechanisms highlighted.