The electronic structure of the organic superconductor beta "-(BEDT-TTF)(2)SF5CH2CF2SO3 (BEDT-TTF is bis(ethylenedithio)tetrathiafulvalene) was characterized with the use of electron spin resonance (ESR) spectroscopy and electronic band structure calculations. The room-temperature ESR line width is 24-27 G in the plane of a donor molecule layer (i.e., in the ab-plane) and similar to 32 G along the normal to this plane (i.e., along the c*-direction). The ab-plane anisotropy of the microwave conductivity was extracted for the first time from the ESR Dysonian line shape analysis. The in-plane conductivity varies sinusoidally, is maximal along the interstack direction (b-axis), and is minimal along the donor stack direction (a-axis). The Fermi surfaces of the title compound consist of a 2D hole pocket and a pair of 1D wavy lines. The directions for the in-plane conductivity maximum and minimum are in excellent agreement with the electronic band structure calculated for beta "-(BEDT-TTF)(2)SF5CH2CF2SO3, and the origin of the in-plane conductivity anisotropy lies in the one-dimensional part of the Fermi surface. This is the first time that an organic conductor shows Dysonian ESR line shape due to its 2D and strongly metallic nature, yet the 1D character is revealed simultaneously through the in-plane conductivity anisotropy.