Recognizing and reporting a transfusion reaction is important in transfusion practice. However, the actual incidence of transfusion reactions is frequently underestimated. We designed an online transfusion reaction reporting system for nurses who take care of transfusion recipients. The common management before and after transfusion and the 18 most common transfusion reactions were itemized as tick boxes. We found the overall documented incidence of transfusion reaction increased dramatically, from 0.21% to 0.61% per unit of blood, after we started using an online reporting system. Overall, 94% (30/32) of nurses took only 1 week to become familiar with the new system, and 88% (28/32) considered the new system helpful in improving the quality of clinical transfusion care. By using an intranet connection, blood bank physicians can also identify patients who are having a reaction and provide appropriate recommendations immediately. A well-designed online reporting system may improve the ability to estimate the incidence of transfusion reactions and the quality of transfusion care.