Dissimilar welding between austenitic stainless steel and high strength low alloy steel (HSLA) have numerous applications such as nuclear, oil and gas, petrochemical, refinery. The most important and widely used types of steel are the AISI 304L and API 5L X65, respectively. Welding of these joints has problems such as residual stresses, undesirable phases and structures. Having a desirable and efficient joint will avoid costly waste of raw materials. Welding of dissimilar austenitic stainless steel joints to low alloy steel due to different properties of the alloy such as melting point, thermal expansion coefficient, chemical composition, etc. is a difficult and difficult process. Most of metallurgical problems of these joints include: segergasion, formation of intermetallic compounds, and the formation of a brittle layer in the low alloy steel joint, which results in loss of mechanical properties. Investigation of the mechanical and microstructural properties of these types of joints is important in design as well as safety. Using a buttering and selecting the appropriate filler metal are some of the parameters that have an important influence on the properties of these joints. In this study, the nickel base buttering of ERNiCr3 with nature was used. So that after the buttering diposited on low alloy API 5L X65 specimens heat-treated for stress relief for one hour at 650°C, Then, using filler metals, the joint operation was completed. To ensure the security of the joints, all welded were examined and verified by radiography testing. After sampling To investigate the microstructural properties, scanning electron microscopy, optical microscopy, and Energy dispersive detector were used. In order to evaluate the mechanical properties of joints,tensile combinatorial and local, impact combinatorial and local,microhardness tests were performed. No blade-shaped structures were observed at the API 5L X65 steel melt boundary and the butter layer, indicating that the butter layer ERNiCr3 diposited was suitable to remove this microstructure. The ERNiCr3 butter layer has a complete austenitic microstructure with Type-I and Type-II Solidfication boundaries. retains its austenitic microstructure despite being dilution 30% than the API 5L X65 base metal. Microstructure of the HAZ in Austenitic Stainless Steel AISI 304L in a Welded Sample with ERNiCr3(W3) Fused to ER308L(W1) and ER309L(W2) Samples had less Grain Growth and the ferrite delta formation. The heat input generated by the W3 sample welding process is lower than the W1 and W2 samples. The filler metal ER308L and AISI 304L steel have created a more continuous interface due to the similarity of the chemical composition. The W3 sample represents the lowest angular distortion (residual stress). The dilution of the buttering in the weld metal lead to changed the chemical composition weld metal and the increase in the percentage of nickel in the zone that resulted in the weld metal W1 and W2 samples of ferrite delta and austenitic structure being observed that made the zone encourage to Solidification Cracking, but no cracking was found in the zone. The most match chemical composition observed in EDS linear analysis was for W1 and W3 samples. The W3 weld zone had the highest hardness due to the formation of complex carbides, NbC and TiC. The highest strength is related to the W3 sample. The smaller HAZ region with finer grains and lower delta ferrite, greater bonding of the weld metal to the primer layer, and higher weld metal alloying elements improved the strength of this sample. The different regions of the W3 sample exhibited the highest impact energy, due to the finer grain heat affected zone, the absence of delta ferrite and full austenitic structure. The fracture surface of the specimens all exhibits a soft fracture, except that the fracture surface of the W3 specimen has deeper and larger clavages, indicating greater ductility of the W3 specimen.