This paper reports the results from an investigation on petrogenesis and geochemistry of the Lemera granite pegmatites in Kivu region of Karagwe-Ankole Belt, D. R. Congo and the related tin ore deposits. Seven granite pegmatite samples were collected from outcrops and analyzed for bulk-rock geochemistry analysis using ICP-MS and XRF spectrometry. The analyzed samples show a relative abundance of Al₂O₃ over Fe₂O₃(T) and MgO (12.95, 0.96, and 0.16, all in wt.%, on average and respectively). The alumina saturation index ranges from 1.33 to 2.05. The abundances of some important rare metals, as well as some related key parameters, are as follows: Sn ((1-138)×10^-6), Ta ((0.20-0.60)×10^-6), Nb ((1-8)×10^-6), Cs ((1.20-3.20)×10^-6), Rb ((3-223)×10^-6), Zr ((7-201)×10^-6), w(K)/w(Rb) (150-272); w(K)/w(Cs) (9.06-23.3); w(Nb)/w(Ta) (3.33-14). The results indicate that the Lemera granite pegmatites crystallized from a fertile, peraluminous, and S-type granitic magma through a fractional crystallization process in a late to post-collisional setting. Mineralization of Sn and Zr of Lemera granite pegmatites is noticed.