Aim of the study: was to assess the efficacy of three different natural herbs on cariogenic microorganisms and determining the effective concentration of these herbs. This study was carried out on green tea, anise and mint (aqueous decoction and aqueous infusion) and the bacteria tested in this study were Streptococcus mutans and Lactobacillus acidophilus.Materials and Methods: Aqueous extract was prepared from each herb in two ways (aqueous decoction and aqueous infusion) and four concentration of either of decoction or infusion were prepared, these concentrations were 1, 2, 3 & 20 g% (g/100 ml). Sensitivity tests were held using disc diffusion method and plates containing both types of bacteria were prepared, each plate was loaded by five discs containing three concentrations of the herbal extract and the positive and the negative controls (Amikacin-disc 30μg and discs loaded by sterile saline).The sensitivity tests were divided into two groups: first group was on Lactobacillus acidophilus, this group were divided into plates containing discs loaded by three concentrations (1g %,2g % and 3g %) of green tea extract, plates containing discs loaded by three concentrations (1g %,2 g % and 3g %) of anise extract, plates containing discs loaded by three concentrations (1g %, 2 g% and 3g %) of mint extract and plates containing discs loaded by the maximum obtained concentration 20 g% from the three herbs. The second group was on Streptococcus mutans and divided in the same way.Results: There were no inhibition zone around any disc loaded with any type of the herbal extracts with it’s four concentrations, no inhibition zone around the negative control (discs impregnated in sterile saline) and the only inhibition zone were obtained around the antibiotic discs (Amikacin-disc 30 μg) which were used as the positive controls.Conclusions: The tested natural herbs (green tea, anise and mint) had no antibacterial ability against Lactobacillus acidophilus or Streptococcus mutans and the concentration of an ordinary cup, doubled, tripled or even 20 times of green tea, anise or mint is not efficient in inhibiting the oral cariogenic bacteria.