This study was carried out to determine the antibacterial effect of green tea, guava leaves, coffee, clove, ginger extracts on the most cariogenic bacteria; Streptococcus Mutans and Lactobacillus Acidophilus. In this study, the bacterial strains were divided into two groups and the cultivation of the plant extracts discs on the culture media was done using the "disc diffusion method". The plant extracts were loaded on Whatman No.1 filter papers (discs) using the automatic micropipette and kept for 30 minutes before use for proper absorption. After that, these filter papers were seeded on the surface of the appropriate culture media for each type of bacteria (Trypticase soy agar for Streptococcus mutans, MRS for Lactobacillus Acidophilus) using sterilized twizer in Petri dishes (plates). Each plate contained plant extract impregnated discs, antibiotic disc (Kanamycin against Streptococcus mutans, Penicillin against Lactobacillus Acidophilus were used as a positive control) and distilled water disc (negative control) for comparison. The samples of the study were divided into two main groups of 125 filter paper discs each, according to the type of the inoculated cariogenic bacteria; B1: Streptococcus Mutans group and B2: Lactobacillus Acidophilus group. Then each group was further subdivided into five equal subgroups of 25 discs each, according to the type of plant extract tested where, E1: green tea extract, E2: guava extract, E3: coffee extract, E4: clove extract and E5: ginger extract. The samples were incubated in the CO2 incubator at 37ºC for 24 hours, then the antibacterial behavior of each plant extract was assessed by measuring the diameter of the inhibition zones around the impregnated discs by millimeters in comparison to the positive control (antibiotic disc) and negative control (distilled water disc) .