40K/40Ar ages are reported from the Marienhof and Billstein Formations in the Rehoboth basement inlier at the southern margin of the Damara Orogen. K-Ar reference lines for Marienhof phyllites sampled close to the Areb shear zone yielded ages between 495,3 ± 5,0 Ma and 532,8 ± 5,3 Ma. Individual mineral ages of white micas from Marienhof quartzites and a single biotite from a Marienhof rhyolite range between 506,4 ± 5,1 Ma and 528,6 ± 5,5 Ma, while individual mineral ages obtained for white micas of the Billstein Formation range between 504,8 ± 5,2 Ma and 519,0 ± 5,5 Ma. The results of this study are in agreement with the results of earlier workers who proposed that folding and metamorphism reached the southern margin of the Damara Orogen at about 530 Ma.