: Recently, the concept of hygiene has been promoted, and many sanitary goods that contain antimicrobial reagents have been produced.Such reagents are divided into organic and inorganic ones.Some literature has pointed out that these reagents have many disadvantages, such as short-time durability of antibacterial effect, degeneration by heating operation, and physical irritation. Furthermore, the organic antimicrobial reagents have intensive antimicrobial action, but long use of these reagents may cause microbial substitution and teratogenicity.We aimed to put inorganic antimicrobial reagent into practical use, and the effects of silver-inorganic antimicrobial reagents (IONPURETM and NOVARON AG 300TM) on oral microorganisms were examined.1. Minimum inhibitory concentrations (MICs) of antimicrobial reagents (IONPURE and NOVAR-ON) for Streptococcus mutans were 7.5 mg/m/ and 1.3 mg/m/. The antimicrobial action was bacteriostatic. The microorganisms on resin plates that contained both antimicrobial reagents were remarkably reduced.2. MICs for Streptococcus mutans on resin plates that contained antimicrobial reagents were 5 wt% (IONPURE) and 10 wt% (NOVARON). 3. Insoluble glucan synthesis was inhibited on NOVARON-containing resin plates. On the other hand, IONPURE was not so noticeable.4. The surviving microorganisms of Streptococcus mutans on resin plates that contained both antimicrobial reagents (3 wt%) were remarkably decreased.These results suggest that IONPURE and NOVARON were effectual antimicrobial reagents against Streptococcus mutans, and that they were useful for antimicrobial prosthesis.