Acid volcanic or hypabyssal rocks from the Bertrab and the Littlewood Nunataks in Coats Land have been dated by the whole-rock Rb-Sr method. Five specimens from the Bertrab Nunatak define an isochron indicating an age of $$998 \pm 19 m.y.$$, based on a value of $$1.39 \times 10^{-11} year^{-1}$$ for the decay constant of $$Rb^{87}$$. Two specimens from the Littlewood Nunataks have possible ages ranging from 966 to 1,035 m.y. and fit the Bertrab isochron within experimental error. A pooled isochron of all the data leads to a best estimate of $$1,001 \pm 16 m.y.$$ for the age of these rocks. The initial $$Sr^{87}/Sr^{86}$$ ratio is $$0.7042 \pm 0.0011$$. A whole-rock K-Ar date of $$840 \pm 30 m.y.$$ reported in the literature shows no evidence of the expected argon loss caused by the Ross Orogeny.