There are numerous studies identifying the presence and toxicity of glucocorticoids (GCs) in water; however, limited studies reported effective GC removal technologies. This study researched the efficiency of calcium peroxide (CaO2) in removing GC in wastewater treatment plants (WWTPs) with triamcinolone acetonide (TA) as the representative. Effects of CaO2 dosage, initial pH, and water matrix were investigated. The functional reactive oxygen species (ROS) during TA removal was tested. Specifically, TA degradation intermediates by CaO2 oxidation were identified for the first time. GC toxicity change during TA removal was deduced. The results indicated that CaO2 treatment can be an effective method for TA removal and toxicity decrease. At the reaction time of 60 min, more than 78% of TA can be degraded with CaO2 at 0.05-4 g L-1. The TA removal efficiency increased with the increase of CaO2 dosage. The optimal initial pH value is 6.8. HCO3-, Cl-, and NO3 -had inhibitive effects on TA removal while SO42- had no effect and PO43- had positive effect. Humic acid (HA) had positive effects on TA removal because of its obvious adsorption effects. The HO center dot and center dot O-2(-) released by CaO2 are the functional ROS for TA removal, among which HO% is the most important one. Besides the oxidation of HO center dot and center dot O-2(-), the adsorption effects of CaO2 and Ca(OH)(2) and the hydrolysis at alkaline conditions may also contribute to TA removal. Six intermediates were revealed during TA degradation, indicating the decrease in GC activity.