The electrochemical behavior of biofilm on AISI 316L stainless steel was studied in the mixed inhibitor system: amino trimethylene phosphonic acid with zinc sulfate (ATMP + Zn2+) added inland water system. The natural biofilm shifts potential toward positive side, about 380 mV vs SCE and in the presence of inhibitor, the biofilm does not shift the potential toward positive side. Cathodic polorization and cyclic voltammogram explained the presence of manganese oxide and peroxide in the natural biofilm. There were no oxidation and reduction peak in the inhibitor treated (industrial) biofilm because of removal of cations in the biofilm by inhibitor. The natural biofilm has thick matrix with extracellular polysaccharides (EPS) on 316L SS. In the presence of inhibitor in the water, distinct rod shaped cells were noticed without any EPS. The inhibitor added system showed the lowest passive current (i(p)) and high resistance (Rct) when compared to the natural biofilm.