The sterilization method of records by fumigation using mixed gas of methyl bromide(MB) and ethylene oxide(ETO) has been generally used as a way to protect biological deterioration by microorganisms and insects. In this study, we confirmed sterilization effect of MB and ETO [86 : 14(Vol.%)] on and analyzed toxicity on microorganisms isolated from records. To analyze sterilization effect of fumigation on microorganisms and insect, we have fumigated microorganisms and insect with a various amounts mixed gas of MB and ETO, and various exposure time. Insect was sterilized at all experimental conditions. In microorganisms, sterilization effect was detected only when the mixed gas was treated at $120g/m^3$ concentration for at least 24 hrs. To test the possibility of isolated microorganisms as a threat to human health, it was investigated that toxicity test using yeast, radish and cancer cells on microorganisms. Only Aspergillus oryzae had an inhibition effect on growth of yeast. radish and cancer cells, respectively. These results demonstrate that sterilization effect can occur at low concentrations of the mixed gas on insect but requires higher concentrations of the mixed gas on microorganisms. In addition to, it is suspected that the possibility of the microorganism as a threat to human health is little.