Statement of Problem: The Strep. mutans, Staph. aureus, Cand.albicans, and Cand. Glabrata are the most common cuases of oral infections and the use of chemical drugs usually leads to drug resistant microorganisms. Purpose: The aim of this study was to investigate the antimicrobial activity of Cinnamon and Eucalyptus oils against this oral microorganism.Materials and Methods: The oils were prepared by steam distillation and their inhibitory activity at different concentrations and the minimum inhibit­ory concentrations (MIC) were determined. Strep. mutans, multi drug resist-ant (MDR) Strep. mutans, Staph. aureus, methicilin resistant staph. areus, Candida. albicans, C.glabrata were used in this study. The data were analyz­ed using Chi square and Fisher statistical test.Results: All of the bacterial and fungal isolates were sensitive to Cinnamon and Eucalyptus. Cinnamon oil showed strong promising inhibitory activity on all the S.mutans isolates at a concentration as low as 3.12%. Eucalyptus oil showed less inhibitory activity, as the least effective concentration of this oil was 25%. The MIC of Cinnamon and Eucalyptus oil ranged 12.8-51.2 and 64-256mg/ml, respectively.Conclusion: Both Cinnamon and Eucalyptus oils exhibited antimicrobial activity but their effectiveness varied. Cinnamon oil showed stronger inhibi­tory activity as measured by MIC determination. S.mutans, the etiological agents of dental caries, were highly sensitive to Cinnamon oil and hence it may be used as an antiseptic in toothpaste, mouthwash or chewing gum for prevention of dental caries and other oral infections. KEY WORDS: Cinnamon; Eucalyptus; S.mutans; S.aureus; MIC