Abstract: Abstract: Objective To investigate the antibacterial effects of two kinds of silver colloid nanoparticles which were prepared with glucose and sodium hypophosphite against standard strain and fluoride–resistant strain of Streptococcus mutans. Methods Two kinds of silver colloid nanoparticles were prepared by reducing silver nitrate with glucose and sodium hypophosphite as reducing agents. We used the disk diffusion method and broth microdilution method to find out the antimicrobial properties of these two silver nanoparticles to standard strain and fluoride–resistant strain of Streptococcus mutans. Results The mean diameters of inhibition zone of the former nanoparticles to test bacteria were 20.87±0.66 mm、19.68±0.86 mm respectively，minimum inhibitory concentrations (MICs）were （2.08±0.90） μg/mL、（2.60±0.90） μg/mL；For the latter nanoparticles，diameters of inhibition zone to test bacteria were （14.86±0.43） mm、（14.19±0.50） mm，MICs were （35.15±12.18） μg/mL、（56.24±24.36） μg/mL. Between the two kinds of silver colloid，antibacterial property of the former was higher than the latter and the difference was quite obvious. There was no significant difference in antibacterial property against standard strain and fluoride–resistant strain in one kind of solution. Conclusion Two kinds of silver colloid nanoparticles made with glucose and sodium hypophosphite as the reducing agents respectively exhibited high antibacterial effects against standard strain and fluoride–resistant strain of Streptococcus mutans，and the former was better than the latter.