Welding has been done by taking mild steel as work piece material in shielded metal arc welding (SMAW) process. Material thickness and current were considered as input parameters. Joining of metals has been completed in two ways. In first process double pass welding has been done in which 1st pass was in reverse polarity and the second pass was in straight polarity and in the 2nd process both the passes of welding were completed with straight polarity. The comparison of microstructure and impact toughness has been investigated. It was found that more amount of heat was generated in the 2nd process as compared to the 1st process. Therefore, growths of grains in heat affected zone occurred and maximum growth occurred in 2nd than 1st process. Impact strength increased with decrease in current value and increase in material thickness respectively. The impact strength values for 1st process welding were relatively less as compared to 2nd process. © International Journal of Mathematical, Engineering and Management Sciences.