The present study is in the aim to evaluate the antioxidative activity of Pistacia lentiscus leaf (PL) extract main components, the activity was examined using the free radical (DPPH•) assay. The HPLC analysis of Pistacia lentiscus leaf extract led to the separation of 27 compounds of which the gallic acid (GA), quercetin (QT), and catechin (CT) were identified as major ones. Concerning the (IC50) inhibition was 0.0068 (mg/ml), 0.0070 (mg/ml), 0.0148 (mg/ml) and 0,0015 (mg/ml) value for gallic acid, quercetin, and catechin, PL leaf extract respectively. Moreover, the interaction of Pistacia lentiscus leaf extract main components with the DPPH• free radicals has been clarified by the theoretical calculations articulated on the density functional theory (DFT), it has been shown that the simulated interaction energy had a negative value of −20.46 Kcal/mol, −18.95 Kcal/mol and −16.19 Kcal/mol respectively for (GA), (QT) and (CT), which approve the above experimental results.