Chemical composition of the essential oils derived from the tested plants A novel method was developed in the present study for accurate GC/MS analysis of the essential oils. This study may facilitate the identification of unknown compounds not included in the library. Results, showing the percentages of the highest possible number of identified components are summarized and listed in Table 1, Fig. (1) and Table 2, Fig. (2, 3) for Artemesia herba alba and A. monosperma respectively. Also, Table (3) illustrated the main difference in composition of the essential oils from A. herba alba and A. monosperma. Twenty compounds identified in A. herba alba essential oil. The principle component of the essential oil was a-Thujone (47.48%), what also reported as the major constituent and dominated of the A.herba-alba essential oil originating (Benjilali et al., 1982, Boukrich et al., 2010, Mighri et al., 2010, Kadri et al., 2011, Aghaei et al., 2011) on the other hand, the major component of this oil differed from that reported by several authors for A. herba-alba oils, in which camphor represent the principle component of the