Objective: Jet-washers are being used to remove dental plaque from the tooth surfaces utilizing force of water jet at home. In a previous study we reported that alkali-ion water (AW) can disintegrate glucan from cariogenic biofilms with or without a driving force (Gyo M et al. IADR, Brisbane, 2006). Therefore, it was hypothesized that AW would influence the removal of cariogenic biofilms by a Jet-washer and thus investigated. Methods: Sucrose dependent biofilms were grown on equal-sized bovine enamel coupons (surface ground with #1200 silicon carbide paper) using four species of oral streptococci (Streptococcus mutans, Streptococcus sobrinus, Streptococcus gordonii and Streptococcus mitis) at 37°C for 20 hrs in an oral biofilm reactor. AW (TK7705, Panasonic, Japan) with different pH levels was used to remove biofilms at two different force levels of a Jet-washer (Doltz, EW1250, Panasonic, Japan) for 10sec and tap water (TW) was used as control. That was followed by quantitative analysis of retained biofilms. SEM observation and Real-time PCR were also performed. Results: In almost all cases biofilms were removed from the contact point of the water jet. On Two-way ANOVA analysis it was found that smaller amounts of glucan and bacterial cells were retained when AW was used compared to TW. SEM photomicrographs also revealed that comparatively more clean enamel surface could be visible in case of AW compared to TW. However, in some cases a large amount of biofilms were removed by TW with the application of Jet-washer. Conclusion: Depending on the application Jet-washer found effective in removing cariogenic biofilms from slightly rougher enamel surfaces. However, in comparison AW appeared to be more influential than TW and that may be effective in terms of caries prevention in the long run. This study was supported by G-COE Program, IRCMSTBD at TMDU and Panasonic Electric Works Co., Ltd. Japan.