Sodium lauryl sulfate (SLS) is an anionic surfactant used in many applications such as cleaning and hygiene products, electroplating, etc. For the first time, effects of SLS as an electroyte additive on electrochemical behavior of positive active material and commercial positive plates have been studied by cyclic voltammetry (CV), eletrochemical impedance measurements. The electrode surface morphology after 20 cycles of CV was studied by using scanning electron microscopy (SEM). Results show that SLS additive significantly improves the conversion reactions of positive active material and therefore enhances charge/discharge capacity. By increasing SLS concentrate, crystalline structure of positive active material changed. The effects of SLS on kinetic parameters of positive electrode reactions are also discussed in this paper. The results showed that SLS is promising for use as electrolyte additive for lead-acid batteries.Keywords: lead-acid battery, positive plate, positive active material, electrolyte aditive, sodium lauryl sulfate.