Formic acid electrooxidation was studied on Bi modified polyoriented and preferential (111) Pt nanoparticles. For both types of nanoparticles, Bi coverage was progressively increased and its effect on formic acid electrooxidation was evaluated using cyclic voltammetry and chronoamperometric measurements. In both experiments, significant and progressive enhancements on the electrooxidation current densities were obtained in comparison to the bare Pt nanoparticles. In voltammetry, at maximum Bi coverage, higher current densities at peak potential were obtained with the preferential (111) Pt nanoparticles (approximately 42 mA cm(-2)) as compared to the polyoriented Pt nanoparticles (approximately 32 mA cm(-2)) in agreement with previous single crystal studies. Nevertheless, this tendency was not observed in chronoamperometry at 0.4 V where currents obtained at maximum Bi coverage were similar. On the other hand, CO poison formation was also evaluated at open circuit potential. The resulting electrochemical activity has been rationalized using different parameters, such as surface structure, size domains, particle size and Bi coverage.