In Gas Metal Arc Welding (GMAW), the applied thermal cycle will cause a change in the chemical composition and structure of the welded zone compared to the base metal (BM). As a result, it causes changes in mechanical properties including fatigue strength. This research investigates the tensile test, hardness, and fatigue properties of A36 low-alloy marine steel with high tensile strength. For this purpose, A36 low-alloy marine steel was welded by the GMAW method. After performing the mechanical tests, the structural examination was done by optical microscope (OM) and Atomic Force Microscope (AFM) on the welded samples. The obtained results show that the fatigue strength of the weld has decreased compared to the base metal by creating coarse and heterogeneous grain structures, which are caused by the effects of the mentioned items in the weld metal. Microstructural defects in the weld metal caused cracks germination and accelerated crack growth. So that the fatigue strength of the weld metal was lower than that of the BM. Manuscript profile