MIG Welding is a process that Permanente joining the similar and non-similar metals by the application of coalescence. The main objective was optimization of microstructural and mechanical properties of HAZ in the Gas Metal Arc Welding (GMAW) of Medium carbon Steel AISI1045 are presented. The experiment used to conduct based on the Design of Experiment (DOE) by adopting the Full Factorial Design by using Taguchi method. L9 Orthogonal array was selected for analysis of data. The research has been done using experimental method with sample size nine .Nine experiments were using welding parameters like current, voltage and speed used as input variables are Tensile strength and Hardness of HAZ as the output response in the investigation. S/N and ANOVA were performed to know the significant of the parameters and the optimal welding conditions using MINTAB 15 software. The maximum mechanical properties of the welded sample were obtained when welding the sample Tensile strength and Hardness of heat affected zone were obtained 233,71Mpa and 39.37HRC and Microstructure examination results show larger grain size in heat affected zone compared to the parent metal. The results obtained from different parameters of current, voltage and speed. . Key words: Metal inert gas (MIG) welding, Micro structure, fusion, Heat Affected zone, Parent Metal, Welding parameters, Medium carbon steel.