In this research, joining of AISI 304 austenitic stainless steel to UNS S32750 super duplex stainless steel using AWS BNi-2 interlayer through transient liquid phase bonding (TLP) has been studied. For this purpose, samples with the size of 10×10×3 mm were prepared, and then the surfaces to be joined were grounded using emery sheets of SiC of grit sizes varying from 240 to 1200. Then, both base metals and interlayer were ultrasonically cleaned in an acetone bath for 60 minutes. Interlayer was placed between the base materials and then this the specimens were put inside a fixture. Bonding of specimens were accomplished under argon atmosphere at 1050 o C and 1080 o C for different bonding times. Specimens were bonded at 1050 o C for 10 and 45 min. Afterward, joints with complete isothermal solidification were homogenized at 1180 o C for 180 min. Then, bonded specimens were cut and prepared for standard metallography. To investigate more details of microstructures, samples were studied by optical microscopy and field emission scanning electron microscopy. Also, distribution of alloying elements at the joint area was studied by using Energy Dispersive Spectroscopy (EDS). Volume friction of ferrite of the duplex stainless steel before and after bonding was estimated using ferritoscope. Finally, mechanical properties of the joints were evaluated using measuring the shear strength and hardness. Results revealed that isothermal solidification was completed for the specimens bonded at 1050 o C and 1080 o C for 45 and 10 min, respectively. Other bonded specimens were consisted of athermally solidification zone (ASZ). The width of athermally solidification zone was decreased by increasing the bonding time and temperature. Alloying elements concentration and microstructural changing were detected at the diffusion affected zones (DAZ) at the base metals and interlayer interface of the bonded specimens. The width of these regions was increased by increasing the bonding time and temperature. The microconstituent formed at the DAZs were evidenced to be borides of alloying elements of the base materials. ISZ was consisted of Ni solid solution and the ASZ was found to be consisted of Ni solid solution phase and borides and silicide microconstituents. Sigma phase was observed in the microstructure of super duplex stainless steel in the specimens cooled in the furnace after bonding. Low volume friction of ferrite in these specimens was confirmed the formation of deleterious phases. Formation of these deleterious phases was prevented by cooling the specimens in the water from the bonding temperature after bonding. Alloying elements concentration at the DAZs was strongly decreased by homogenizing of the specimens with complete isothermal solidification. But some voids were appeared at the DAZ of super duplex stainless steel due to Kirkendall effect. Microhardness examination at the bonding zone of the bonded specimens indicated the mean hardness value was increased at the ASZ and DAZs. Mean hardness value of the centerline of the joint was decreased from 546 to 365 HV by increasing bonding time due to isothermal solidification completion. Shear strength of the bonded specimens was increased by increasing bonding time and temperature. Changing cooling ambient from furnace to water has not significant effect on shear strength of the joints. Shear strength of the homogenized specimen was decreased due to the voids at the joint. Maximum shear strength (380 MPa) was achieved for the specimens with complete isothermal solidification and about 0.7 shear strength of duplex stainless steel.