For several decades, the electrical admittance has been very useful for the determination of physical quantities, such as the characterization of some electrical properties of interest in organic samples. In this work, an electrical system based on graphite electrodes to determine the amount of living biomass of the cyanobacteria Fischerella sp. is proposed. Cyanobacteria are phototrophic microorganisms with applications on bioremediation, pharmaceutics, medicine, among others. The strain was characterized in BG-11 medium and cultured at different biomass concentrations. Samples were evaluated by electrical admittance and contrasted by the technique of dry weight in order to correlate the results registered by the/a proposal electric circuit. Scanning frequencies from admittance went in an order from 10 Hz to 1 000 000 Hz. Also, they showed a reproducibility, getting deviations of 6.45 × 10-5. This electrical system can be used to evaluate Fischerella sp. living biomass concentrations with high reliability.