Objectives : The purpose of this study is to analyze the sterilizing effects of toothbrushes by administering bacteria into toothbrushes and reproducing the antibacterial effects using a microwave oven. Methods : The heads of four-row mid-strength toothbrushes were cut, put in a bacterial solution ($3{ imes}10^9cells/ml$) for vortexing, and sterilized with microwaves for 0, 30, and 60 seconds. They were then moved into four tubes containing DW 10 ml and suspended in a vortex mixer for two minutes to separate bacteria from them. DW 9ml was added by 1ml of bacteria for dilution of $10{sim}10^6$ times. It was then administered to the BHI agar plate by 0.1ml and cultured at $37^{circ}C$ for 24 hours. Total number of bacteria adhered to a toothbrush was obtained by multiplying the number of colonies by the dilution factor. The experiment was done in the first, second, and third step, being repeated in a normal temperature drier ($23^{circ}C$) after 5, 9 and 24 hours. Results : The results of the experiment revealed that the sterilizing effects were 95% or over. When toothbrushes were sterilized for 60 seconds, the number of colonies is about 11 after drying for 5 hours, 7 after drying for 9 hours and 2 after drying for 24 hours. The sterilizing effects reached 98% when the bacteria-administered toothbrush was sterilized for 1 minute after drying for 24 hours. Conclusions : The results demonstrated that toothbrush sterilizing by using microwave is a suitable way to prevent cross-contamination of toothbrushes by oral bacterial infection and thus easy to use at home. However, this study suggests that toothbrush sterilizing by using microwave should be limited within two times a week because the physical properties of toothbrush might be changed.