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The Kid plutonic suite in southeast Sinai, Egypt is composed of: (1) a gabbro-diorite complex; (2) quartz monzodiorite; (3) granodiorite-monzogranite association; (4) syenogranite. Major- and trace element analyses and radiogenic isotope data (Rb/Sr, Sm/Nd and Pb/Pb) are presented for these rocks. Rb-Sr isochrons indicate ages of 581 +/- 11 Ma, 576 +/- 11 Ma and 570 +/- 4 Ma for the quartz monzodiorite-granodiorite-monzogranite association and syenogranite, respectively. The gabbro-diorite complex is a layered intrusion varying in SiO2, From 42 to 59 wt%. It shows a calc-alkaline trend, and the trace element characteristics of are lavas. Subsequently, this magma fractionated to give quartz monzodiorite and syenogranite magmas. The quartz monzodiorite has low initial Sr-87/Sr-86 ratios (0.703) and high epsilon(Nd) values (+4.4 +/- 0.3), with trace element characteristics of volcanic-are granites. The granodiorite-monzogranite association has higher initial Sr ratio (0.7044), lower epsilon(Nd) (+1.5-+2.7) and relatively high Pb-207/Pb-204 and Pb-208/Pb-204; significantly different from those of the older rocks. Isotopic data and REE modelling suggest that it formed by partial melting of an early Pan-African amphibolitic lower crust. The syenogranite is a typical highly fractionated post-orogenic granite, with a deep negative Eu anomaly, HFSE and REE enrichment, a Sr-87/Sr-86 initial ratio of 0.7033, epsilon(Nd) of 4.5 +/- 0.5 and distinct variations in the Pb-206/Pb-204 ratio. The isotopic compositions of Sr, Nd and Pb indicate that the syenogranite and the quartz monzodiorite are comagmatic. Increasing fluorine concentration from the quartz monzodiorite to the syenogranite suggests that fluid fractionation involving fluorine complexing played an important role in the genesis of the syenogranite. This process led to the enrichment of HFSE and HREE, to extensive fractional crystallization, to changes in the U/Pb ratios and a distinct variation in (206)/(PbPb)-Pb-204.