The presence of hormones in water represents a risk to the aquatic environment, especially due to the fact that these compounds are not effectively degraded by the traditional biological processes employed in wastewater treatment plant (WWTP). This work aimed to determine an optimum condition of the peroxidation process assisted by UV-C irradiation (λ = 254 nm) for the degradation of the hormone 17 α-ethinylestradiol (EE2) present in aqueous solution, in addition to the ecotoxicological evaluation. Synthetic EE2 samples (C₀ = 1000 μg L⁻¹) were treated using different processes: photolysis, peroxidation ([H₂O₂]₀ = 25 mg L⁻¹), and UV/H₂O₂ ([H₂O₂]₀ = 25, 50, and 75 mg L⁻¹). Photolysis and peroxidation in isolation were ineffective for degradation of the hormone in aqueous solutions, while the UV/H₂O₂ treatment provided total degradation of the compound, under the conditions employed. For real effluent samples from an WWTP, the UV/H₂O₂ process provided EE2 degradation efficiency of almost 100%, applying a photon flux of 2.76 kJ L⁻¹ and with [H₂O₂]_consumed = 42.5 mg L⁻¹. The kinetic parameters for the UV/H₂O₂ treatment showed that the use of higher initial concentrations of peroxide resulted in slower degradation. Evaluation was made of the acute (considering immobility) and chronic (considering survival and reproduction) ecotoxicological effects of the treated effluent on the cladoceran Ceriodaphnia silvestrii. In the acute toxicity tests, an EC₅₀ (48 h) value of 53.97% was obtained. The chronic toxicity tests revealed an adverse effect on reproduction, with an EC₅₀ (8 days) value of 21.54%.