Abstract: Periodontal disease is a global public health problem, including in Malaysia. The destruction of the periodontium has been associated with subgingival plaque microflora. Prevotella intermedia has been categorized as a periodontopathic bacteria as it contributes to the development and progression of periodontal disease. Therefore, a study on P.intermedia�s virulent properties is important for the understanding of periodontal disease. Thus, the aim of the study is to characterize the virulence effect of the intracellular toxin. In the study, intracellular toxin of P.intermedia from ninety isolates were obtained and injected subcutaneously in male balb/c mice, aged between 8-12 weeks old. The results showed that the intracellular toxin from all P.intermedia isolates were able to cause the development of localized lesions on the skin of balb/c mice when 0.1, 0.2 and 0.3 mL filtrates were used. In addition, it was found that the degree of skin lesions on the balb/c mice was dose dependent as the infective dose was found to correspond to the development of larger lesion accompanied by skin coagulative necrosis. In the second part of the study, the intracellular toxin was heated for 1, 5, 15, 30, 45 and 60 min at different temperatures of 37 and 60 C prior to the infection in mice. It was discovered that the intracellular toxin was not stable and sensitive towards high temperature and is thermolabile when the activity was terminated upon heating to 60 C as none of the injected mice developed skin lesion.