A computerized potential-modulated ESR (PMESR) technique has been developed with the emphasis on spectral separation for two paramagnetic species coexisting in the same potential region. Potential-dependent spin-spin broadening, ESR peak shift due to signal superimposition and their influences on spectral subtraction are discussed in detail. A formula of the prerequisite for effective PMESR is presented. The power of this technique is demonstrated by successfully decomposing the ESR signals contributed from TEMPO radicals both in solution and in Nafion(R) coating into the component spectra.