An oxidative fumigant is potent to kill insect pests infesting stored grains. Its oxidative activity generates reactive oxygen species (ROS), which has been considered to be a main insecticidal factor. Furthermore, the oxidative fumigant has cytotoxic effect to insect cell lines, but the cytotoxicity is abrogated by antioxidant treatment. This study aimed to extend the usefulness of the oxidative fumigant in terms of medical purpose against cancer cells. Five cancer cell lines HCT 116 (human colorectal), Lovo (human colorectal), SW480 (human colorectal), MDA-MB-231 (human breast), and MCF-7 (human breast) were tested to determine their susceptibility to the oxidative fumigant with reference to two insect cell lines (Sf9 and Hi-Five). All cancer cell lines were highly susceptible to the oxidative fumigant, compared to the insect cell lines. Interestingly, basal ROS levels of the cancer cell lines were much higher than the insect cell lines. Furthermore, the oxidative fumigant significantly increased the ROS levels in the cancer cells. Treatment of vitamin E as an antioxidant mitigated the cytotoxicity of the oxidative fumigant. Thus, the high susceptibility of cancer cells to the oxidative fumigant may be induced by their high inducible ROS production. This study also investigated the antiviral activity of the oxidative fumigant against insect and plant viruses. The oxidative fumigant significantly inactivated a baculovirus (dsDNA virus) by inhibiting polyhedral production in Sf9 cells. It also inactivated tobacco mosaic virus (ssRNA virus) by suppressing phytopathogenicity. These results support a broad effect of the oxidative fumigant, which can be applied to agricultural and medical purposes.