Many scientists have elucidated that characteristics of micro-nanobubbles are distinctly different from those of normal bubbles. However, the physicochemical properties of micro-nanobubble water have not been sufficiently examined. In the present study, in order to generate free radicals by self-collapse phenomenon of micro-nanobubbles, an ESR measurement was conducted. As a result, micro-nanobubbles collapsed only with any physical forces while the self-collapse phenomenon of the micro-nanobubbles was not observed in the experiment.