In this study, the effect of bonding temperature and bonding pressure on deformation and tensile properties of diffusion bonded joint of STS304 compact heat exchanger was investigated. The diffusion bonds were prepared at 700, 800 and $900^{circ}C$ for 30, 60 and 90 min in pressure of 3, 5, and 7 MPa under high vacuum condition. The height deformation of joint decreased and the width deformation of joint increased with increasing bonding pressure at $900^{circ}C$. The ratio of non-bonded layer and void observed in the joint decreased with increasing bonding temperature and bonding pressure. Three types of the fracture surface were observed after tensile test. The non-bonded layer was observed in diffusion bonded joint preformed at $700^{circ}C$, the non-bonded layer and void were observed at $800^{circ}C$. On the other hand, the ductile fracture occurred in diffusion bonded joint preformed at $900^{circ}C$. Tensile load of joint bonded at $800^{circ}C$ was proportional to length of bonded layer and tensile load of joint bonded at $900^{circ}C$ was proportional to minimum width of pattern. The tensile strength of joint was same as base metal.