Welding materials, that the principal chemical component is nickel, are used usually for the welding between copper and austenitic stainless steels. But many kinds of mechanical or physical properties of welds between two materials will change largely. In this study, Functionally Graded Piping Joints (FGPJ) have been manufactured as an experiment using copper and austenitic stainless steel (SUS304) powder by a process based on HIP. This composition has been confirmed by absorbed electron and characteristics X-ray images of each mixed layer for FGPJ to be uniform or continuous. The following items have been investigated and compared with the linear law of mixture rule: Vickers hardness, thermal expansion, and thermal conductivity at a one-dimensional non-steady state etc. Those physical properties have been identified to depend on the mixing ratios of copper and austenitic stainless steel (SUS304). Pretty good agreements have been obtained between the experimental data and the calculated values according to the linear law of mixture rule.