In combustion chamber of liquid propellant launch vehicle, the inner shell of the chamber is copper alloy with cooling channels for regenerative cooling and outer shell is steel to maintain high pressure inside the chamber. The purpose of this study is to find the optimum condition for diffusion bonding of copper and steel and the experimental conditions were 3 different pressures at temperatures from 800 degrees C to 950 degrees C. In order to characterize the flow strength of materials at high temperatures, several tensile tests were performed at several temperatures from 800 degrees C to 950 degrees C. This information is used to estimate the test condition for diffusion bonding and superplastic forming. Mechanical properties of bonded specimen were evaluated with single lap joint tests and shear tests. Microstructure of bonded layer has been also observed with SEM with EDX. It is shown that the optimum condition of diffusion bonding is 7 MPa at 890 degrees C, for one hour. Pressurization test of bonded specimen with cooling channels was performed with hydraulic pressure of 87 MPa without failure.