Simultaneous reduction of carbon dioxide and nitrate ions was examined at gas-diffusion electrodes with various catalysts (Cr, Mo, Mn, Ru, Co, Rh, Lr, Ni, Pd, Pt, Cu, Ag, Au, Zn, Cd, In, Tl, Sn, and Pb). The formation of urea, CO, formic acid, nitrite ions, and ammonia at the gas-diffusion electrodes with group 11-14 catalysts, : except for Au, was found in the simultaneous reduction. The maximum faradaic efficiency of urea formation on Zn catalysts is approximately 35% at -1.75 V.The formation of urea at the gas-diffusion electrodes with groups 6-10 catalysts was not found in the simultaneous reduction of CO2 and nitrate. Relationship of the ability for urea formation to the ability for CO and NH3 formation was investigated with various catalysts. The ability for urea formation with the catalysts depends on the ability for CO and NH3 formation. The catalysts with high ability for CO and NH3 formation could form large amounts of CO-like and ammonia-like precursors. The faradaic efficiency of urea formation for simultaneous reduction with nitrate ions is lower than that with nitrite ions. This result seems to be related to the ability for ammonia-like precursor formation.