The intake of dietary antioxidants is associated with the prevention of cardiovascular diseases, cancer and aging, by acting against oxidative stress caused by free radicals. Olive (Olea europaea L.) leaves are considered a source of bioactive compounds with antioxidant properties. In this context, the present study aimed to evaluate the potential of olive leaf extract (OLE) to scavenge reactive oxygen species (ROS) and reactive nitrogen species (RNS). The commercial antioxidant ascorbic acid was used as reference compound. The extract was obtained from micronized powder olive leaves in methanol/water (80/20%) in ratio 1:20 (w/v) after removal of hexane soluble compounds. After lyophilization the extract was resuspended in PBS (phosphate buffered saline), pH 7.4. The in vitro scavenging activity of OLE was assessed against superoxide anion (O2•-), hypochlorous acid (HOCl) and nitric oxide (NO•). Results are expressed as mean ± standard deviation of six different experiments. The statistical analysis was performed using a one-way ANOVA followed by t-test (p<0.05). OLE showed effective in vitro inhibition of all reactive species studied. Scavenging activity of OLE against O2•- and NO• resulted IC50 values of 52.6 ± 2.1 microgram/mL and 48.4 ± 6.8 microgram/mL, respectively, with no significant differences for ascorbic acid activity (59.3 ± 9.2 microgram/mL and 43.9 ± 8.8 microgram/mL, respectively). Nevertheless, OLE was less effective in scavenging HOCl when compared to the reference ascorbic acid, with IC50 values of 714.1 ± 31.4 microgram/mL and 27.3 ± 1.3 microgram/mL, respectively. The results obtained in the present study clearly suggest that OLE may be effective antioxidant in biological systems, preventing oxidative stress, based on its scavenging activity against ROS and RNS.