Many studies determined effect of plant extract on plant pathogens and human pathogens. Alhagi maurorum is considered as one of the important medicinal plants in Iraq. It is used for urinary tract infection, rheumatic pains and liver disorders. Study the Inhibition Effect of Alhagi extract on oral microorganisms as Streptococci, Actinobacillus and Staphylococci, with (0, 10, 50 and 100 percentages). The concentrations of 0% has not any inhibition effect, 10%, has a slight inhibition effect against oral Streptococci and Actinobacillus, but has not effect on Staphylococci. 50%, has an inhibition effect against oral Streptococci more than E-coli, but has not effect on Staphylococci, but 100%, has a wide inhibition effect a against oral Streptococci more than Actinobacillus except Staphylococci has not effect. The lack of inhibition effect at the concentration of 0% and 10% of Alhagi maurorum aqueous extract may be returned to the limits or decline of active components in these low concentrations of aqueous extract. In addition, studies indicate that there are many factors have an effect in the minimizing the impact of plant extracts.