Bismuth compounds are used in the treatment of gastrointestinal infections due to its effectiveness against Helicobacter pylori as Gram-negative bacteria. Moreover, the nanometric materials show better biological properties that the materials in block. The aim of this study was to determine the MICs (minimal inhibitory concentrations) of three colloidal dispersions of bismuth nanoparticles compared with silver nanoparticles against oral and nosocomial bacteria. The nanoparticles were synthesized by chemical reduction in DMSO. The MICs of each colloidal dispersion were obtained on eight species representative of the subgingival biofilm, as well as in three species of medical importance: Staphylococcus aureus, Pseudomonas aeruginosa and Escherichia coli. All bismuth compounds showed antimicrobial effect on the tested bacterial species, with MICs between 37 to 329 µg/mL. On the other hand, AgNPs showed MICs from 16 to 32 µg/mL for the bacteria of subgingival biofilm and from 32 to 65 µg/mL for the species of medical importance. In accordance with this study, the different BiNPs had an antimicrobial effect in all the bacterial species, although with a potency lower than AgNPs. to the dental surface by means of specific molecules [5,6], such as Streptococcus spp and Actinomyces spp. Then, the bridge settlers or secondary bacteria, which include species like Fusobacterium nucleatum,