This study is concerned with the radioactivity and mineralogy of the younger granites and pegmatites in the Wadi Haleifiya area, southeastern Sinai Peninsula, Egypt. The area is occupied by metasediments, migmatites, older and younger granites. Most of these rocks, especially granites, are dissected by mafic and felsic dykes as well as pegmatites. The younger granites are represented by three main varieties: monzogranites, syenogranites and alkali feldspar granites. The monzogranite consists essentially of quartz, plagioclase, potash feldspar and biotite with minor musco-vite. Iron oxide, titanite, zircon and allanite are the main accessory minerals. Syenogranite is massive, medium- to coarse-grained and commonly exhibits equigranular and hypidiomorphic textures. It is made up essentially of potash feldspar, quartz, plagioclase and biotite. Iron oxides, allanite, epidote, titanite, and zircon are accessory minerals. The alkali feldspar granite consists mainly of perthite, quartz, alkali amphibole (arfvedsonite and riebekite), biotite, sub-ordinate plagioclase and aegirine. Iron oxide, zircon and apatite are accessory minerals, whereas chlorite and sas-surite are secondary minerals. The altered monzogranite and pegmatite recorded high radioelement contents. The eU reaches up to 120 (av.=82×10-6) in the altered monzogranite and up to 55 (av.=27×10-6) in the pegmatites. The high radioactivity in the altered monzogranite is due to the presence of thorite, uranothorite and metamict zircon. In the pegmatites, it is re-lated to the presence of uranophane, uranothorite, thorite, zircon, samarskite, monazite, xenotime, magnetite, ilmen-ite, hematite and rutile. This study is concerned with the radioactivity and mineralogy of the younger granites and pegmatites in the Wadi Haleifiya area, southeastern Sinai Peninsula, Egypt. The area is occupied by metasediments, migmatites, older and younger granites. Most of these rocks, especially granites, are dissected by mafic and felsic dykes as well as pegmatites. The younger granites are represented by three main varieties: monzogranites, syenogranites and alkali feldspar granites. The monzogranite consists essentially of quartz, plagioclase, potash feldspar and biotite with minor musco-vite. Iron oxide , titanite, zircon and allanite are the main accessory minerals. Syenogranite is massive, medium- to coarse-grained and commonly exhibits equigranular and hypidiomorphic textures. It is made up essentially of potash feldspar, quartz, plagioclase and biotite. Iron oxides, allanite, epidote, titanite, and zircon are accessory minerals. The alkali feldspar granite consists mainly of perthite, quartz, alkal i am amphibole (arfvedsonite and riebekite), biotite, sub-ordinate plagioclase and aegirine. Iron oxide, zircon and apatite are accessory minerals, including chlorite and sas-surite are secondary minerals. The altered monzogranite and pegmatite recorded high radioelement contents. The eU reaches up to 120 (av. = 82 × 10-6) in the altered monzogranite and up to 55 (av. = 27 × 10-6) in the pegmatites. The high radioactivity in the altered monzogranite is due to the presence of thorite, uranothorite and metamict zircon. In the pegmatites, it is re-lated to the presence of uranophane, uranothorite, thorite, zircon, samarskite, monazite, xenotime, magnetite, ilmen-ite, hematite and rutile.