Rb-Sr whole-rock age determinations on four suites of samples from the Awasib Mountain terrane in southern Namibia yield estimates consistent with the suspected Middle to Late Proterozoic origin of this crustal segment. Isochrons from the Aunis Granodiorite-gneiss and Haiber Flats Formation basaltic andesite give ages and initial 87Sr/86Sr ratios (Ro ) of 1 271 ± 62 my, 0.7029 ± 3, and 1086 ± 44 my, 0.70305 ± 17, respectively. The estimated age of 1 038 ± 74 m.y. and Ro of 0.718 ± 15 for a rhyolite porphyry from the Haiber Flats Formation are within error of those deduced for the basaltic andesite, but have been derived from an errorchron. The younger, possibly subvolcanic, Awasib Granite yields an errorchron with an apparent age of 934 ± 70 m.y. and Ro of 0.719 ± 12. It seems likely that heterogeneity in the latter may be attributable to compositional variation in a postulated crustal source.