The effect of heat input from laser beam welding (LBW) on the microstructral and mechanical properties of superalloy Inconel 718 were investigated. Four different heat input produced to evaluate the geometry of weld seams. Full penetration was achieved in all weld experiments. The analysis of optical and field emission scanning electron microscopy together with microhardness based on ISO 9015-2:2003(E) was performed. Increasing the amount of heat input from 74.5 J/mm through 126.5 J/mm changed the resulting weld shape from a wine glass shape to a stemless wine glass shape with wider surface bead widths. The effect of heat input was significantly clear at the widths of the mid- and upper-side of the weld seam. It was observed that the differences of the heat input affected the solidification rate. The the solidification rate was determined as approximately approximate to 4.65x10(5) degrees Cs(-1) for the weld samples applied the highest heat input. The hardness property of the weld samples decreased with the increasing the heat input. The hardness range of the weld samples applied the heat input were between 280 +/- 10 HV(0.2) and 255 +/- 8 HV(0.2) indicating the effect of heat input significantly. The secondary dendrite arm spacing increased with increasing heat input. The tnicrostructure of weld metal became more refined with smaller dendrite arm spacing as the heat input was decreased.