Background: The risk of transfusion-transmissible infections (TTIs) of HBV, HCV, and HIV in Korea has been reduced significantly by strengthening the blood safety policies. On the other hand, the risk of TTI still exists due to the diagnostic window period or viral variants. Methods: The residual risks of TTI of HBV, HCV, and HIV were calculated from July 1, 2012 to June 30, 2018 by dividing the data into two year sets. The residual risk was conducted by separating the donors who donated only once and those who donated more than once during each period. Results: In the first two years, the residual risks of HBV, HCV, and HIV were calculated to be 17.54/10 6 , 0.42/10 6 , and 0.30/10 6 respectively. The residual risk of HBV and HCV over the last two years was calculated to be 9.41/10 6 and 0.27/10 6 , showing a tendency to decrease with time. On the other hand, the residual risk of HIV over the last two years was calculated to be 0.29/10 6 , showing no significant difference. The residual risk in the donors who donated only once was higher than that in the donors who donated more than once during each period. Conclusion: The real transfusion-transmitted infection can be different from the estimated residual risk in this study because this study was based on the thesis that all NAT-reactive blood components cause infection. Because the residual risk of HBV is higher than HCV and HIV, it was considered that the safety measures for the HBV need to be improved continuously.