The electrocatalytic activity of synthesized quasispherical Pt nanoparticles (NPs) has been studied, taking as a model the COads electrooxidation reaction in two imidazolium-based ionic liquids such as 1-butyl-3- methylimidazolium bis(trifluoromethylsulfonyl)imide [C4mim+][NTf2−] and 1-butyl-3-methylimidazolium tetrafluoroborate [C4mim+][BF4−]. In particular, the effect of (i) watercontent, (ii) temperature, and (iii) nature of the roomtemperature ionic liquid (RTIL) on the electrocatalytic behavior of these Pt NPs has been systematically evaluated. The obtained results show how important are those parameters, since the COads oxidation peak potential exhibits a great sensitivity depending on the water content, temperature, and nature of the RTIL used. Interestingly, the charge density associated with the COads electrooxidation peak strongly dependson the nature of the ionic liquid, which reflects the complexity of this electrocatalytic reaction in this media. Moreover, Pt NP electrocatalyst degradation in those RTILs, considered as a loss of electrochemically active area, has been evaluated and shows high stability despite the extreme potentials afforded in RTILs.