This research evaluated the influence of different washing treatments (i.e., tap water, ozone, microbubbles, and ozone combined with microbubbles) on post-harvest decay of chestnuts (Castanea crenata ‘Tsukuba’) during storage. Overall, treatments with ozone and microbubbles significantly reduced the decay frequency and the associated microbial populations (aerobic bacteria, mold/filamentous fungi, and yeasts) during post-harvest storage compared with the traditional practice (tap water washing). Enhancing the efficacy of chestnut washing treatments will contribute to the improved storage of high-quality chestnuts.