The aim of this study was to evaluate the antiplaque effect of Ocimum gratissimum (Og) by in vivo investigation. Fifteen healthy volunteers participated in a crossover, double-blind clinical study, using a 3-day partial-mouth plaque accumulation model. The participants abolished any method of mechanical oral hygiene and they were randomly assigned to initially use just the following mouthrinses: distilled water (DW solution), 0.12% chlorhexidine digluconate (CLX solution) or 10% Og (Og solution). The plaque index (PLI) was recorded in all mandibular teeth at the end of the trial and the Kruskal-Wallis (α=0.05) and Mann-Whitney (α=0.05) tests were used to estimate the difference among groups. The clinical results showed statistically significant difference among the groups (p<0.05), favoring the CLX solution and Og solution, but the first was more effective (p<0.05). The mouthrinses containing 0.12% chlorhexidine digluconate and 10% Og were able to inhibit plaque re-growth, however Og showed more limited results in comparison to CLX.