Objective:Chlorine dioxide(CD) gas has been used as a fumigant in the disinfection of biosafety labo-ratories.In this study,some experiments were conducted to assess the inactivation of spores inoculated on six ma-terials [stainless steel(SS),painted steel(PS),polyvinyl chlorid(PVC),polyurethane(PU),glass(GS),and cotton cloth(CC)] by CD gas.The main aims of the study were to determine the sporicidal efficacy of CD gas and the effect of prehumidification before decontamination on sporicidal efficacy.Methods:Material coupons(1.2 cm diameter of SS,PS,and PU;1.0 cm×1.0 cm for PVC,GS,and CC) were contaminated with 10 μl of Bacillus subtilis var.niger(ATCC 9372) spore suspension in mixed organic burden and then dried in a biosafety cabinet for 12 h.The spores were recovered by soaking the coupons in 5 ml of extraction liquid for 1 h and then vortexing the liquid for 1 min.Results:The log reductions in spore numbers on inoculated test materials exposed to CD gas [0.080%(volume ratio,v/v) for 3 h] were in the range of from 1.80 to 6.64.Statistically significant differences were found in decontamination efficacies on test material coupons of SS,PS,PU,and CC between with and without a 1-h prehumidification treatment.With the extraction method,there were no statistically significant differences in the recovery ratios between the porous and non-porous materials.Conclusions:The results reported from this study could provide information for developing decontamination technology based on CD gas for targeting surface microbial contamination. Objective: Chlorine dioxide (CD) gas has been used as a fumigant in the disinfection of biosafety laboratories. In this study, some experiments were conducted to assess the inactivation of spores inoculated on six ma-terials [stainless steel (SS), painted steel (PS), polyvinyl chlorid (PVC), polyurethane (PU), glass (GS), and cotton cloth (CC)] by CD gas. The main aims of the study were to determine the sporicidal efficacy of CD gas and the effect of prehumidification before decontamination on sporicidal efficacy. Methods: Material coupons (1.2 cm diameter of SS, PS, and PU; 1.0 cm × 1.0 cm for PVC, GS, and CC) were contaminated with 10 μl of Bacillus subtilis var. niger ATCC 9372) spore suspension in mixed organic burden and then dried in a biosafety cabinet for 12 h. The spores were recovered by soaking the coupons in 5 ml of extraction liquid for 1 h and then vortexing the liquid for 1 min. Results: The log reductions in spore numbers on inoculated test materials exposed to CD gas [0.080% (volume ratio, v / v) fo r 3 h] were in the range of from 1.80 to 6.64.Statistically significant differences were found in decontamination efficacies on test material coupons of SS, PS, PU, ​​and CC between with and without a 1-h prehumidification treatment. Since the extraction method , there were no significant significant differences in the recovery ratios between the porous and non-porous materials. Conclusions: The results reported from this study could provide information for developing decontamination technology based on CD gas for targeting surface microbial contamination.