Objective: The aim of this an in vitro study was directed to compare the anti-bacterial effects between herbal extract of Acacia fruits and Acacia leaves on Streptococcus mutans and Lactobacillus acidophilus bacteria. Subjects and methods: 90 samples of tested material (acacia fruits and acacia leaves extracts) and control group were equally divided into 3 groups. The 30 samples of each group were subdivided into 2 equal subgroups; one to test the material antibacterial against Streptococcus mutans and the other to test the material antibacterial against Lactobacillus acidophilus bacteria. Results: It was found that Amoxicillin have the highest antibacterial effect with highly significant difference in compared to other groups. While acacia fruits came second followed by acacia leaves respectively. However there are high significant differences between all groups except that between acacia fruits and acacia leaves against Lactobacillus acidophilus bacteria which showed equal antibacterial activity. Conclusion: Amoxicillin still has the highest antibacterial effect. Although the Acacia nilotica fruits and leaves extracts had higher antibacterial activity; further studies and modifications are needed before use of these extracts as antibacterial in humans.