The present paper deals with the problem of voltammetric determination of a mixture of amine-type antioxidant N-phenyl-1-naphthylamine (PNA) and phenol-type antioxidant butylated hydroxytoluene (BHT) in oil matrix by the method of linear sweep voltammetry using gold working electrode. Attention was focused on the effect of large excess of PNA on the curves of anodic oxidation of BHT. It was found that only more than tenfold excess of PNA disturbs the determination of the phenol-type antioxidant in the adopted supporting electrolyte. In such case it is necessary to reduce its content by its transformation into the corresponding nitrosamine by reaction with nitrous acid. The rate constants of this reaction were determined for two different concentrations of PNA.