Cathodic denitrification using a bioelectrochemical system removes nitrogen at a low C/N ratio, and also harvests energy as electricity. Denitrifying biocathodes were cultured using three electrode systems with nitrate (NO₃⁻) and/or nitrite (NO₂⁻) as electron acceptors. Results showed that denitrification of NO_x⁻ in biocathodes exhibit typical enzymatic reaction kinetics and denitrification rate follows the Monod equation, with r_max = 1.33 kg N m⁻³ d⁻¹, K_s = 5.52 g L⁻¹ for NO₃⁻ and r_max = 1.76 kg N m⁻³ d⁻¹, K_s = 8.09 g L⁻¹ for NO₂⁻, respectively. Optimal cathodic efficiency was obtained at an initial substrate concentration of 0.5 g L⁻¹. A high-throughput sequencing analysis of 16S rRNA gene showed high biodiversity in a denitrifying biocathode and nitrite contributed more to the formation of cathodic microbial community structure. Denitrification functional gene analysis revealed Pseudomonas are effective denitrifiers in a biocathode.