Two pulses of granitoid magmatism occurred in the Cordillera Real in the eastern Andes of Bolivia (La Paz department), one in the Middle to Upper Triassic and the other in the late Oligocene to Miocene. This magmatism occurred along the southward extension of the rift-controlled inner magmatic arc of the southeastern Andes of Peru. The peraluminous chemistry, the high but restricted silica range, and the low CaO and MgO contents of these “S-like” plutonic rocks suggest that they formed by fractional crystallization followed by variable assimilation of supracrustal rocks. The Pb isotopic data of Tilton and others (1981) supports a mantle component in the Cordillera Real melts. The Cordillera Real granites are characterized by high tin contents. Geochemical indicators such as TiO 2 content and Rb/Sr, Rb/Ba, and Mg/Li ratios suggest that the tin was introduced by assimilation during the late and post-magmatic stages of the plutons.