The effect of temperature on antibacterial activity of betel leaves extracts was determined by the methods as described by Lee et al. (2004) 27. Ethanol extract (10 g/ml) of betel leaves were prepared with 95% ethanol and transferred into different vials. The vials with the betel leaf extract and the negative controls were incubated in shaking water bath (GFL 1083, German) set at 37oC, 50oC, 75oC, and 100oC, respectively, for 30 min. The heated betel leaf extracts were cooled down and stored at 4oC until use. The antibacterial activity was assayed by the method as described before.