The air oxidation of three Co-Ta alloys containing 15, 30 and 45 wt.%Ta was investigated with a thermobalance at 600 degreesC, 700 degreesC and 800 degreesC. In all tests the oxidation kinetics followed the parabolic rate law with the exception of Co-45Ta alloy oxidized at 800 degreesC. The activations energies were found to be quite close for Co-15Ta and Co-30Ta alloys (127,32 and 128,39 kJ/mol, respectively), while for Co-45Ta it was not possible to calculate its activaton energy due to the non-parabolic behaviour of 800 degreesC test. The oxidation morphologies of Co-15Ta and Co-30Ta alloys are very similar. An external scale of Co3O4 characterizes them for 600 degreesC and a duplex Co3O4/CoO scale for 700 and 800 degreesC, accompanied by an internal oxidation zone (IOZ), in which both metallic phases suffered oxidation. The Co-45Ta alloy displayed a different morphology characterized by an external monolayer of CoO for 600 degreesC and 700 degreesC and Co3O4 for 800 degreesC, and an IOZ where only the Ta-rich phase was oxidized.