A Study on microstructural changes of sensitized Alloy 600 which was rapidly solidified by a $CO_2$ laser beam was conducted using microscopic equipments such as SEM and TEM. Dissolution of Cr-rich carbides and resultant Cr recovery on the grain boundaries occurred in the heat affected zone (HZA). The microstructure of the laser melted zone (LMZ) having epitaxially solidified from the HAZ was mainly celluar-dendritic with the 〈100〉 crystallographic direction of growth. The Cr concentration was observed to increase along the cell bondaries, and tiny particles were distributed along the cell walls with tangled dislocations around them. Cr-rich carbides had been completely melted by the high density of a laser beam, and were not re-precipitated during the matrix solidification due to a fast cooling rate in the LMZ.