ion In this work microstructure characteristic, mechanical properties and corrosion behavior of dissimilar welding of UNS S32750 superduplex stainless steel (SDSS) to API X65 high strength low alloy (HSLA) were investigated. The gas tungsten arc welding process with direct electrode negative polarity (GTAW-DCEN) was used for welding with AWS A2594N as the filler metal. Since heat input plays an important role in welding of SDSS, the welds were produced in four different heat inputs and the effects of heat input on microstructure evolution, mechanical properties and corrosion resistance of weld zone were investigated. The microstructures of welded joints were investigated using optical microscope (OM) and scanning electron microscope (SEM). The mechanical property of weldments was investigated byCharpy impact test at -20 o C and then surfaces of fracture were evaluated by SEM and EDS scanning.The corrosion resistance was evaluated through potentiodynamic and cyclic polarization tests in 3.5% NaCl solution at ambient temperature. Also potentiodynamic polarization in several temperature tests was used for investigation of critical pitting temperature (CPT) of weld metals with 0.78 and 0.86 KJ/mm heat input. Zero resistance ammeter (ZRA) tests also were used for investigation of behavior of galvanic corrosion on API X65/ weld metal with highest properties. The results showed that an increase in the heat input in a range of 0.5-0.86 KJ/mm can lead to decrease of the weld metal ferrite content from 44% to 34%. A heat affected zone with about 200 micrometer width and lowest austenite compare with base metal and weld metal was created in SDSS base metal. M But in heat affected zone of HSLA base metal in low heat inputs beinite and ferrite phases and in high heat inputs perlite and ferrite phases were created respectively. The results of charpy impact tests investigated that two weldments with low heat inputs were berittle and discontinuous respectively and weldments with high heat inputs were higher strength than base metals. In addition EDS scanning from fracture surface showed that weld metal with highest heat input had high alloy particle. According to the potentiodynamic polarization tests, behaviors of weld metals were alike SDSS base metal and presented excellent corrosion resistance comparing HSLA base metal. Cyclic polarization tests investigated weld metal with the highest heat input had the highest sensitive to pitting corrosion. The results of potentiodynamic polarization tests at several temperatures showed pitting potential decrease with increase of temperature and also 65 and 35 o C determined as CPT of weld metals with 0.78 and 0.86 KJ/mm heat input respectively. According to the results determined that welding in 0.78 KJ/mm heat input can lead to weld metal with higher impact energy and excellent corrosion resistance. The results of ZRA investigated that galvanic corrosion was created in couple of HSLA/ weld metal with the best properties and the mechanism of corrosion was pitting corrosion. Key Words: Superduplex Stainless Steel, High Strength Low Alloy, Dissimilar Welding