Performance tests on the gaskets for the knife-edge-type flanges have been carried out for three different materials, namely, Ag-bearing OFC (oxygen-free copper), Zr-bearing OFC and original OFC as a reference. The tests were made by checking helium leak through the joints with the test gaskets before and after high-temperature baking and by measuring the size of the grooves made on the gaskets by joining. The results have shown that the gasket made of 0.02% Zr-bearing OFC with 10% cold work exhibits the most superior characteristic among the three materials, especially when the joints are subjected to high-temperature baking. This is probably due to the fact that the hardness change in the Zr-bearing OFC is very small in the measured temperature range between room temperature and 400°C in comparison to those of the other two materials.