Two forms of pegmatite have been distinguished (segregations and dikes) hosted in the cataclastic rocks, at the Abu Rusheid area, southeastern Desert of Egypt. The cataclastic rocks covering an area about 2 km² , and composed of (from base to top); protomylonite, mylonite, ultramylonite, and quartzite with gradational contacts. The segregations are unzoned, flat lenses, less than 1 m, while the dikes, usually of the zoned type, have (2-15 m in length, and 0.3 m in width), trending NNW-SSE and dipping 10-30?/ WSW parallel to banding of the cataclastic rocks. Albitization, chloritization, fluoritization and silicification are the major alteration processes in the cataclastics and pegmatites due to the effect of hydrothermal solution. The total REE content in the pegmatite ranges from 44 to 824 ppm with 342 ppm as the average. LREE is more enriched than the HREE in the pegmatite (?LREE/?HREE =7.8) and related to the presence of allanite-(Ce) and monazite-(Ce). Hydrothermal alteration during post-magmatic stages is shed light on the development of M-type tetrad effect in the REE pattern. The rare metals-bearing minerals such zircon, monazite - (Ce), allanite - (Ce), Nb-Ta minerals (columbite-(Fe) and euxenite-(Y), base metals (pyrite and molybdite), beryl and radioactive minerals (thorite, uranophane, torbernite and kasolite) have been found in the pegmatites. Isoconcentration maps show abnormal contents of Nb,Zr, Y, Pb, eU and eTh, and could be considered as low grade ores. The Abu Rusheid pegmatites show low-CaO content (1 % av.), high Fe/Mg ratio (5.9 av.), enrichment of HFSE (Nb, Zr, Y,U, Th), peraluminous, A-type post-orogenic tectonic setting and their mineral composition supporting the NYF nature of the pegmatites.