It has been generally accepted that, due to high ionization potential values, single electron transfer followed by proton transfer (SET-PT) is not a plausible mechanism of antioxidant action in flavonoids. In this paper the SET-PT mechanism of quercetin (Q) was examined by revealing possible reaction paths of the once formed quercetin radical cation (Q⁺˙) at the M0-52X/6311+G(d,p) level of theory. The deprotonation of Q⁺˙ was simulated by examining its chemical behavior in the presence of three bases: methylamine (representative of neutral bases), the MeS anion (CH₃S⁻) and the hydroxide anion (representative of anionic bases). It was found that Q⁺˙ will spontaneously be transformed into Q in the presence of bases whose HOMO energies are higher than the SOMO energy of Q⁺˙ in a given medium, implying that Q cannot undergo the SET-PT mechanism in such an environment. In the reaction with the MeS anion in both gaseous and aqueous phases and the hydroxide anion in the gaseous phase Q⁺˙ accepts an electron from the base, and so-formed Q undergoes the hydrogen atom transfer mechanism. On the other hand, SET-PT is a plausible mechanism of Q in the presence of bases whose HOMO energies are lower than the SOMO energy of Q⁺˙ in a given medium. In such cases Q⁺˙ spontaneously donates a proton to the base, with energetic stabilization of the system. Our investigation showed that Q conforms to the SET-PT mechanism in the presence of methylamine, in both gaseous and aqueous phases, and in the presence of the hydroxide anion, in the aqueous solution.