Background: Marjoram belongs to the Lamiaceae family of plants is common in most parts of the world as a medicinal plant used.

Objective: The aim of this study was to identify and compare the essential oil of two Origanum species to determine their composition is the most important.

Methods: The aerial parts of two species of plants belong to Origanum genus, including Origanum vulgare L. and Origanum majorana L. in July 2013, in the beginning of flowering stage, were collected from the farm research of Medicinal Plants Institute. The aerial parts were dried in shadow condition in room and then after the essential oil content and its components were measured. The essential oils were extracted by clevenger apparatus and its constituents were determined by GC-MS.

Results: The results indicated that amount of essential oil in O. vulgare was 0.13% (v/v), and its main components were trans-caryophyllene (21.46%), germacrene D (18.99%) and (E, E-α) farnesene (9.12%). While amount of essential oil in O. majorana was 1.09% (v/v), and its main components consisted of terpinolene-4-ol (23.11%), γ-terpinene (13.94%) and α-terpinene (8.11%).