Abstract: Anti-Helicobacter pylori effects of leaves of Ocimum basilicum L. (sweet basil, Lamiaceae) and Ocimum basilicum var. purpurascens (purple basil, Lamiaceae) were evaluated. Macerated aqueous and methanol extracts were tested against 45 clinical isolates of Helicobacter pylori using paper Disc Diffusion Method (DDM) on modified egg yolk emulsion agar (EYE agar). Although there were small differences in sensitivity among the isolates tested, but all isolates were susceptible to methanol and aqueous extracts. The Minimum Inhibitory Concentrations (MIC) of the extracts from leaves of sweet basil and purple basil were 677 and 729 μg mL-1, respectively using agar dilution method. Antibacterial constituents of sweet basil extract were stable after one month of storage at 4°C but lost 31% its activity after 4 weeks at room temperature. The extract preserved its activity when heated to 80°C for 30 min and autoclaved at 121°C for 20 min. It was stable at pH 5-8.