Electrochemical reduction of CO2 dissolved in 0.1 M NaCl solution was investigated at boron-doped diamond (BDD) modified by various metals. Iridium, platinum, and copper were used as the modifying metals. The metals were deposited on the BDD surface by using chronoamperometry technique at each potential reduction of the metals, i.e. +0.6 V (vs. Ag/AgCl) for iridium, -0.2 V for platinum, and -0.4 V for copper. SEM images were used to characterize the modified electrodes. The electrochemical reduction of CO2 was performed in 100 mL 0.1 M NaCl containing saturated CO2 at the potential of -2.5 V (vs. Ag/AgCl). Characterization of the electrolysis results using GC and HPLC indicated that the products formed at the modified electrodes were the combination of electrochemical results at BDD and at the modifying metals. However, in addition to the combination products, formaldehyde (3.81 ppm) and acetate (22.5 ppm) were observed at copper-modified BDD, suggested a synergic effect occurred between BDD and copper.