The NW-trending elongation of the all topographic ridges in Gabal El Sibai area draw present author`s attention. As well as the differential elongation directions of the oval-shaped granitoid masses exposed in the study area trending to NNW-SSE, NW-SE and WNW-ESE directions in the eastern (as Delihimmi and Humrat Ghannam masses), central (Um Shaddad and El Sibai-Abu El Tiyur masses) and southern (Um Luseifa mass) parts of the mapped area, respectively. Field study revealed that, the area is covered by an ophiolitic mélange comprising allochthonous dismembered blocks and fragments of serpentinites and related rocks. Metagabbros and metavolcanics, as well as arc-metavolcanics and related volcanogenic metasediments enclosed in a mélange matrix composed of metagrywackes and actinolite-biotite and graphite schists. Hammamat series, represent the extension of the known Wadi Kareim basin, unconformably overlie the ophiolitic mélange along the most northwestern part of the area. The intrusive rocks are represented by syn-tectonic Um Luseifa granodiorite pluton, younger gabbros and late-tectonic granites represented by Delihimmi, Um shaddad, El Sibai-Abu ElTiyur and Humrat ghannam plutons. The analysis of structural events affecting G. El Sibai area revealed the presence of at least three phases of deformations. The tectonic evolution of the area started with an early phase of collisional tectonics causing low angle thrusting and ductile type deformations comprising D1 and D2 deformations of structural elements trending NE-SW and E-W or ENE-WSW and WNW-ESE directions, respectively. The last deformation phase (D3) is dominated by a complex of subparallel and en echelon major NW-SE trending sinistral strike-slip faults. They are associated with all features and characteristics of braided fault zones similar to the NW-SE trending Najd Shear System (NSS) of the Arabian Shield. The probable extension of these NSS into the central Eastern Desert was first illustrated locally (in Hamrawin area) by Abu Zeid (1984), later confirmed in G. El Shalul area (Ahmed, 2002), and its regional extension was first suggested by Stern (1985) and Sultan et al. (1988).