Reactive oxygen species (ROS) contribute to pathogenesis of many human diseases including Parkinson’s and Alzheimer's diseases, cancer, and diabetes. There is a crucial need for using fully noninvasive imaging to further evaluate the role of ROS in pathogenesis and the potential treatment strategies. Our previous phantom studies demonstrated that ROS containing unpaired electrons can be detected with endogenous CEST and T1 weighted contrasts. However, in vivo detection of ROS using MRI has not yet been demonstrated. This study therefore aimed to demonstrate the feasibility of in vivo ROS detection using endogenous MRI.