The microstructures and mechanical properties of a family of sputter-deposited Cu 1Ϫx Ta x (0 Ͻ x Ͻ 0.18) alloys have been investigated. The as-deposited microstructures for all film compositions consisted of a polycrystalline, face-centered-cubic (fcc) Cu matrix, with varying levels of Ta in solid solution, plus a very high density of discrete, 1 to 3 nm, fcc Ta particles. Decreased deposition temperature (Ϫ120 ЊC vs 100 ЊC) increased the level of Ta in solid solution. After annealing (900 ЊC for 1 hour) the as-deposited 6 at. pct Ta films, the Cu matrix grains remained submicron and the Ta particles remained fcc with no apparent particle coarsening. Additionally, the fcc Ta particles were found before and after annealing to be oriented identically with the Cu matrix and aligned on {111} and {100} habit planes. Annealing 17 at. pct Ta films at 900 ЊC for 1 hour resulted in the formation of body-centered-cubic (bcc) Ta particles (Ͼ50-nm diameter) in addition to the much smaller fcc Ta particles. Annealing the low and high Ta composition films at 900 ЊC for as long as 100 hours produced no observed change in either the Cu matrix grain size or the size and distribution of the fcc and bcc Ta particles. Microhardness and nanoindentation mechanical property evaluations of bulk hot-pressed materials indicated that the high strengths of the composites were unchanged, even after annealing for 100 hours at 900 ЊC.