Microstructure development during MIG welding of copper with iron filler has been studied to gain insight to the process of dissimilar welding. The microstructure of the iron rich bids consist of martensitic bcc iron with cellular network of fcc copper. The scale of network depends on the processing conditions. However, the average composition remains fairly uniform with 20at% Cu excepting at the boundary regions of the bid and the copper plates. A characteristic banded structure could be observed in these regions whose width scales with traverse speed. Evidence of phase separated copper globule suggests access to the submerged miscibility gap and significant undercooling of the melt during welding.