Sputter deposited MoSi2 coatings (200 and 400 nm thick) on copper have been studied in an attempt to prevent or at least reduce the oxidation of copper. Samples were exposed to an air ambient at temperatures ranging from 600-850 degrees C for up to 15 min. Sputter-deposited MoSi2 was amorphous upon deposition and crystallized on annealing. Silicon from the MoSi2 was found to diffuse into the copper causing the MoSi2 to transform to lower silicides. The primary oxidation product for MoSi2-coated samples was CuO (with small amounts of Cu2O), which is in contrast to uncoated copper where Cu2O is the main oxidation product. The amount of copper consumed by oxidation, for a 200 nm MoSi2 barrier relative to uncoated copper, was reduced by approximate to 140 times at 600 degrees C and approximate to 30 times at 800 degrees C. A 400 nm MoSi2 coating yielded an improvement of approximate to 420 times at 600 degrees C, and approximate to 200 times at 850 degrees C. For the 400 nm barrier exposed to air for 15 min, this corresponds to a 35 nm CuO layer at 600 degrees C and a 300 nm thick oxide layer at 850 degrees C.