Riboflavin (Vitamin B 2), one of the most important hydrosoluble vitamins, is a constitutive part of two coenzymes: flavin mononucleotide (FMN) and flavin adenine dinucleotide (FAD), being involved in redox processes occuring in humans. Using chemilluminescence system luminol -hydrogen peroxide, in Tris-HCl buffer, pH=8.5, in the present study the action of different concentrations of Cys, Arg, Lys and His upon the antioxidative activity of the riboflavin has been evidenced. It was found that Cys, Arg, Lys increase while, Arg decreases the riboflavin antioxidative activity. The effect of these amino acids upon the riboflavin fluorescence has also been investigated. A reaction mechanism is also proposed and the results are discussed with relevance to the redox processes of riboflavin.