The Heat-Affected Zone (HAZ) is the region of base metal which has its microstructure altered by welding. Microstructural changes affect the composition of the weldment and need to be controlled since the weld failures are directly related to the microstructure of the Heat affected Zone. This paper is focused on the study of the Gas Metal Arc Welding (GMAW) parameters on the Heat Affected and Weld metal Zone microstructures of industrial low carbon steel (0.20 % C). In order to achieve the aim of the paper, Scan Electron Microscope photos have been used at the Heat Affected and weld metal Zones, some phases are identified. Microstructural analyses of the experimental results of the welded joints confirmed that the welding parameters and heat input are affected the weldment structure in terms of the grain types and character of the structural phase.