Flavin derivatives catalyze the oxidation-reduction reactions in biological systems. All the known flavins form thermodynamically reversible systems. Hence flavins are good candidates for electron transfer mediators. In the present investigation riboflavin (vitamin B-2) is attached to the surface of glassy carbon by covalent linkage. The electrode thus modified is characterized by cyclic voltammetry and impedance measurements. From the voltammetric data the surface coverage is calculated to be 7.7 x 10(-9) mol/cm(2) From the data of the impedance measurements, k degrees for the electron transfer across the modified electrode is calculated to be 2.5 s(-1) and the value is comparable to that obtained from voltammetric data. The modified electrode is tested for its catalytic properties by investigating the reduction of oxygen and the oxidation of ascorbic acid.