E-cigarettes have gained popularity since their introduction in the market; however, only limited data about free radical content of e-cigarette aerosols and the nature of the radicals formed are available in the literature. The overall goal of this study was to characterize and quantify short-lived radicals produced in e-cigarette aerosol condensate and compare them with radicals produced in smoke of combustible cigarettes. To achieve this goal, we employed a spin-trapping method in combination with Electronic Paramagnetic Resonance (EPR) detection. We quantified production of short-lived radicals in e-cigarette aerosol condensate and have shown that they are at the level of 2.2% - 3.7% of the radicals trapped from smoke of a reference 1R6F combustible cigarette. The major component of the spin-adduct spectra was assigned to an oxygen-centered alkoxy radical.