Urine is a good source of biomarkers for clinical proteomics studies. However, one challenge in the use of urine biomarkers is that outside factors can affect the urine proteome. Prednisone is a commonly prescribed glucocorticoid used to treat various diseases in the clinic. To evaluate the possible impact of glucocorticoid drugs on the urine proteome, specifically disease biomarkers, this study investigated the effects of prednisone on the rat urine proteome. Urine samples were collected from control rats and prednisone-treated rats after drug administration. The urinary proteome was analyzed using liquid chromatography-tandem mass spectrometry (LC-MS/MS), and proteins were identified using label-free proteome quantification. Differentially expressed proteins and their human orthologs were analyzed with bioinformatics methods. A total of 523 urinary proteins were identified in rat urine. Using label-free quantification, 36 urinary proteins showed expression changes after prednisone treatment. A total of 17 proteins and/or their human orthologs have been previously annotated as disease biomarkers. After functional analysis, we found that the pharmacological effects of prednisone were reflected in the urine proteome. Thus, urinary proteomics has the potential to be a powerful drug efficacy monitoring tool in the clinic. Meanwhile, alteration of the urine proteome due to prednisone treatment should be considered in future disease biomarker studies.