The aim of this study was to evaluate a rapid spectrophotometric method that measures the OH radical scavenging factor using rhodamine B (RhB) as a means of predicting the removal efficiency of target compounds in a UV/H2O2 process. The OH radical scavenging factor differs considerably among water sources and affects the efficiency of removal of target compounds by the UV/H2O2 process, so an accurate measurement of this factor is important. In this study, RhB was used as an OH radical probe to permit rapid and easy measurement of the OH radical scavenging factor using the R-OH,R-UV concept (R-OH,R-UV-RhB method). A synthetic solution test showed a difference of only 4.7% between the theoretical and measured scavenging factors using the R-OH,R-UV-RhB method, which represents the high accuracy of this method. The degradation rates of three selected pharmaceuticals (sulfamethoxazole, iopromide, and ibuprofen) were then measured in three different natural water sources, and the experimental results were compared with the model prediction value obtained using the R-OH,R-UV-RhB method. Under all 27 test conditions, the average deviation between the experimental and prediction results was less than 6.5%. These results confirmed the accuracy and usefulness of this rapid spectrophotometric method for prediction of the removal efficiency of target compounds by the UV/H2O2 process. (C) 2013 Elsevier B.V. All rights reserved.