Nowadays, plants have become one of the promising sources of chemical compounds that are used in several applications especially in the medicinal. This study aims to illustrate the variability of the chemical composition and the antibacterial activity essential oils of two endemic species in Morocco: Origanum grosii Pau & Font Quer and Origanum elongatum (Bonnet) Emberger & Maire. Each species was collected from two different altitudes in the same region “Taounate" (Morocco). The chemical composition as well as the antibacterial activity of essential oils extracted from dried plants via hydrodistillation was evaluated. Gas chromatography-Mass spectrometry (GC-MS) results showed that the essential oils contain forty-three components, representing around 99% of the total oil for all the tested samples. Carvacrol and Thymol are major compounds for both species. Staphylococcus aureus had a higher sensitivity for the first altitude in both species (MIC=MBC=1.3mg/mL), while Pseudomonas aeruginosa and Acinetobacter baumannii were the higher sensitive for the second altitude with (MIC=MBC=2.5mg/mL). In the light of these findings, Knowledge of the chemical composition and antibacterial activity of essential oils with environmental factors (altitude, edaphic, climatic and genetic factors…) is a very important quality criterion for their marketing and contributes to their valorization as a source of antibiotics after testing its toxicity on humans.