A sheet of carbon felt employed as an electrode exhibits characteristic voltammteric waves for the electrolysis of solutions reflecting a three-dimensional fiber structure of the electrode, in which the solutions both inside and outside the felt electrode undergo electrolysis. The electrolysis behavior can be characterized by three parameters: A(out) for the electrolysis of the outside solution, and l and A(in) for that of inside solution. A(out) expresses the effective outer surface area, and l and A(in) the average distance between the carbon fibers and the effective total surface area of the fibers constituting the felt electrode, respectively. it is shown that chronoamperometry provides a useful means of determining these parameter values. The value of A(in)/m, 0.33 m(2)/g, (m is the mass of the felt electrode) is in the range of the reported values for the surface area per unit weight of carbon felts, and l is in fair agreement with the average distance between the fibers measured with an optical microscope, it is shown that A(in) and l are important parameters determining the rate of bull; electrolysis of a eh en volume of stirred solution, and that A(in) is a key parameter determining the magnitude of the current for biocatalyst-assisted electrolysis.