The study aimed to determine the in-vitro inhibitory effect of Cinnamomum zeylanicum Blume (cinnamon) and Eugenia caryophyllata (clove) oils on combined Porphyromonas gingivalis and Fusobacterium nucleatum biofilm. Following a steam distillation extraction technique, oils from cinnamon bark and clove buds were tested for their antibacterial anti-adhesion and anti-biofilm activities on mixed biofilm containing P.gingivalis and F.nucleatum. The quantification of viable and adhered bacterial cells on 96-well plates using the crystal violet test was analysed and morphology of the bacteria in biofilm was observed under the scanning electron microscope (SEM). Our study demonstrated C.zeylanicum oil inhibited satisfactory anti-adhesion effect and significantly disrupted the biofilm formation at 1.25-5.0 mg/mL whereas E.caryophyllata oil suppressed the adhesion of bacteria and disrupted the formation of biofilm at 0.63-5.0 mg/mL. The SEM study showed prominent changes including ruptures and flatten bacterial wall in samples with E.caryophyllata oil while pitted and flatten cells were seen in C.zeylanicum samples compared to the smooth and distinguished cell wall seen in untreated samples or even more damaged cells in Ampicillin samples. We conclude that C.zeylanicum and E.caryophyllata oils showed significant in vitro anti-biofilm properties against mixed P.gingivalis and F.nucleatum biofilm and prominently altered the bacterial wall morphology. This finding may suggest potential therapeutic properties of these oils in controlling biofilm-related oral diseases. 2019 Journal of International Dental and Medical Research.