Systematic mineralogical chemical compositional variations across a mafic dyke at the Wadi Lethi area, in southern Sinai, are observed. This dyke extrudes the Neoproterozoic Younger Granite of southern Sinai. New petrographic, geochemical data, and mineral chemistry data are applied to predict the evolution scheme of this dyke. The collected samples vary in composition from (outward zone) basalt to (inward zone) andesite. The studied samples exhibit a wide uniform variation in main oxides and trace elements content and display a significant inward chemical variation. The studied samples are mainly identified into basalt, trachy-andesite, basaltic andesite, and andesite. The geochemical characters reveal that the investigated dyke originated from calc-alkaline magma under orogenic tectonic setting. Mineral chemistry data reveals that the studied dyke formed at water pressure ranges from 1-3 kbr and low oxygen fugacity conditions. The fractional crystallization process is assumed to have prevailed during the extrusion of the investigated dyke.