Abstract:This study aimed to evaluate the in vitro antimicrobial activity of synthetic capsaicin and in natura capsaicin against Aggregatibacter actinomycetemcomitans,and compare them with each other. The in natura and synthetic extracts of capsaicin at the concentrations of 0.1%, 0.5%, 1.0%, 1.5%, 2.0%, 2.5% and 3.0% were diluted in 1mL of dimethylsulfoxide (DMSO). The positive control was chlorhexidine 0.12% and the negative control was DMSO. The diameter of the zone of bacterial inhibition was measured after 72 hours. The main effect of capsaicin (natural vs. synthetic) origin against Aggregatibacter actinomycetemcomitans was not significant; No effect of interaction between capsaicin origin and concentration on bacterial growth was observed. Capsaicin presented in vitro antibacterial activity against Aggregatibacter actinomycetemcomitans, with no difference between in natura and synthetic type, but its effect at the concentrations tested was lower than that of chlorhexidine 0.12%. It was concluded that capsaicin presented antimicrobial activity on Aggregatibacter actinomycetemcomitans, irrespective of origin.