The aim of this study was to evaluate the effect of mouthrinse products containing deep sea water. We used original deep sea water(DSW) and processed deep sea water desalinated by reverse osmosis at one time(DDW-1), by reverse osmosis at two times(DDW-2) and concentrated by reverse osmosis(CDW). We made 2 kinds of mouthrinse products containing CDW and other agents for smell and taste and one product without deep sea water. The negative control was distilled water. In vivo study, the dental plaque index scores and the gingival index scores were reduced after 4 weeks mouthrinsing three times daily with 4 kinds of deep sea water and 3 kinds of mouthrinse products(p<0.05). The pH of dental plaque in 1 minute after mouthrinsing was not higher than 5.5 in all solutions, but the pH in 20 minutes after mouthrinsing was higher than 5.7 in DSW, CDW and 3 kinds of products which had higher mineral contents. In vitro study, the mouthrinse solutions containing the higher mineral contents were also the more effective in reduction of methyl mercaptan which is one of the causes of halitosis. The 2 kinds of products containing deep sea water killed Streptococcus mutans(ATCC 25175) in culture plates in one minute. These results indicate the usability of deep sea water in mouthrinses for oral hygiene management.