The present invention relates to fluorescent or luminescent probe reagents for measuring oxidative stress in a cell or an organism. Examples of the probe reagents include: a fluorescent or luminescent protein and a marker protein a fluorescent or luminescent protein, a marker protein, and a regulatory factor or a fluorescent or luminescent protein, a marker protein, a cleavage sequence, and a regulatory factor. In the probe reagents, the marker protein makes it possible to detect the oxidative stress caused by reactive oxygen species and comprises a regulatory factor-binding site and a ubiquitin-binding site and the regulatory factor is a protein making it possible to regulate degradation of the marker protein in response to the reactive oxygen species. The present invention also relates to a method of measuring oxidative stress in a cell or an organism, or a method of screening a substance which suppresses or promotes the oxidative stress in a cell or an organism by using the probe reagent.
