The processing of a copper canister for the final disposal of spent nuclear fuel causes oxidation of the canister surface as the spent fuel will increase its temperature. The maximum surface temperature can be close to 100 °C. The oxide film on copper may protect from corrosion or increase the corrosion rate. Corrosion was studied using weight loss tests. The baseline corrosion rate was determined by using long-term interval tests at room temperature and the effect of temperature was studied using short-term tests at temperatures up to 80 °C. The test environments were synthetic groundwater with total dissolved solids of 10070 mg/l and pH = 8 and bentonite clay pore water with total dissolved solids of 3360 mg/l and pH = 10. Both waters were tested under air and nitrogen purging. After 40 months of immersion at room temperature, the corrosion rates in groundwaters were 4-6 µm y^-1 and in pore waters less than one µm y^-1. At elevated temperatures, the corrosion rates increased with increasing temperature. The highest corrosion rates at 80 °C were 60-80 µm y^-1 in air-purged groundwater and about 30 µm y^-1 in nitrogen-purged groundwater. In air-purged pore water, the highest corrosion rates at 80 °C were 8-9 µm y^-1 and in nitrogen-purged waters 2-4 µm y^-1. In most of the tests, the air-formed oxide films protected from corrosion or did not affect corrosion. Only in the nitrogen-purged pore waters did the oxide films sometimes increase the corrosion rate. The corrosion rate increases were only a few µm y^-1, and this was concluded not to have a significant effect on the copper canister lifetime.