An electrochemical method was applied in order to obtain a new antioxidant for soy biodiesel conservation, from the technical CNSL (tCNSL). The electrochemical modification occurred in an electrolytic tank under controlled conditions, including the voltage, electrical current and tCNSL flow. Physico-chemical analysis and Fourier Transform Infrared (FTIR) were carried out on tCNSL and eCNSL, while Gas Chromatography coupled to Mass Spectrometry (CG-MS) and Nuclear Magnetic Resonance (NMR) was carried out only on eCNSL to characterize the occured transformations after the electrolysis process. The Rancimat results showed that when eCNSL was added to the soy biodiesel, it was able to increased it is oxidative stability and the Induction Period (IP = 7.31 +/- 0.20) values were higher than that required by ANP (Agency of Petroleum, Natural Gas and Biofuels). The electrolytic tests results combined with GC-MS displayed a significant decrease in the cardanol percentage which can promote the formation of dimers or oligomers that may be responsible for the increased antioxidant activity of the eCNSL. Therefore, the electrolysis process resulted in an effective biofuel antioxidant that presents interesting commercial advantages. (C) 2014 Published by Elsevier Ltd.