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The instability and rapid consumption of H 2 O 2 limit the application of UV/H 2 O 2 in water treatment. Recently, calcium peroxide (CaO 2 ) has been demonstrated as an effective source of H 2 O 2 . However, the performance and mechanism of UV/CaO 2 are still unknown. Herein, UV/CaO 2 and UV/H 2 O 2 were compared for degradation of aniline. The removal efficiency of aniline by UV/CaO 2 was slightly lower than that by UV/H 2 O 2 , which could be attributed to the light scavenger by CaO 2 suspended particles. HO‧ was identified to participate in aniline degradation in both UV/CaO 2 and UV/H 2 O 2 , while O 2 - · was only involved in UV/CaO 2 . The efficiency of aniline degradation in UV/CaO 2 was affected by the released H 2 O 2 in the system. The release and decomposition rate of H 2 O 2 in UV/CaO 2 system were influenced by the CaO 2 dosage and reaction pH, but slightly related with water matrix. Excessive CaO 2 would scavenge aniline degradation through the released H 2 O 2 to react with HO‧. Acidic condition would enhance the concentration of H 2 O 2 in UV/CaO 2 and promote the degradation of aniline. Cl - showed slight and almost no effect on aniline degradation in UV/CaO 2 and UV/H 2 O 2 systems, respectively, while HCO 3 - scavenged aniline degradation in UV/CaO 2 . NO 3 - inhibited aniline degradation in both UV/CaO 2 and UV/H 2 O 2 . Compared to UV/H 2 O 2 , UV/CaO 2 shows the similar efficiency on organics removal but conquers the limitations in UV/H 2 O 2 , which is a promising alternative choice in water treatment., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2020 Elsevier Ltd. All rights reserved.)