The essential oils obtained by steam distillation from Moroccan oregano (Origanum compactum, lemon (Citrus limon) and Moroccan thyme (Thymus broussonetti) were analyzed for their chemical composition by gas chromatography. These essential oils were then used in two concentrations (0.05% and 0.1%) in refined olive oil in 6 trials and a control to study the antioxidant properties. The antioxidant activity of the essential oils was followed up by the determination of the peroxide value and the acid value of the olive oil over a period of 6 months. Sensory evaluations of the trials were also conducted by a taste panel of 6 assessors for an organoleptic assessment. Results showed a wide variation in the antioxidant activity of the three oils, and also a slight variation between the two concentrations was observed. The highest activity was observed with thyme oil followed by oregano oil, while an organoleptic quality improvement was obtained with the oregano and lemon oils.