Aqueous methanol extracts of Chemlali olive stones were analyzed by reverse phase high-performance liquid chromatography (HPLC) with diode array detection and mass spectrometry [LC-MS/MS]. Oleoside, oleoside 11-methyl ester, nuezhenide, oleoside 11-methyloleoside, nuezhenide 11-methyloleoside, oleuropein, and glycosides of tryosol and hydroxytyrosol glycosides were identified in stones of Chemali olives. The antioxidant activity observed for the extract of the olive stones (IC50 = 13.84 μg/mL, TEAC = 0.436 mM) may be due to the high content of phenolic compounds, of which the main compounds are nuezhenide (325.78 mg/100g), methoxy derivative of nuezhenide (132.46 mg/100g), and nuezhenide-11-methyloleoside (82.91 mg/100g). These results suggest the use of olive stones as sources of natural antioxidants.