The redox state of mitochondria is one indicator of the functional state of the organelles. Mitochondria are also the primary endogenous source of reactive oxygen species (ROS). Therefore, the redox state of the organelles also reflects their function in ROS production. Here, we provide step-by-step protocols for live-cell imaging and quantification of mitochondrial redox state using the genetically encoded fluorescent biosensor, mitochondria-targeted redox sensing GFP (mito-roGFP), and mitochondrial ROS using the membrane-permeant small molecule dihydroethidium (DHE) in budding yeast cells. For complete details on the use and execution of this protocol, please refer to Liao et al. (2020c).