Laser beam welding is a necessary and helpful tool in modern production technology. It provides low and located heat input, narrow weld widths, high welding speeds and weld depths. Nevertheless, in the weld metal and the surrounding area the microstructure and the mechanical characteristics can be changed afterwards. A decrease of strength and fatigue life is a possible result. To realize a manipulation or control of the weld metal’s microstructure during the welding process is a great challenge. Improving the strength as well as the homogeneity of mechanical properties and chemical composition are the aims of this approach. With indirect introduced ultrasonic amplitudes, the weld pool dynamics and the solidification are affected. The investigation focusses on the effects in the microstructure of high power (8 kW) laser beam welded stainless steel (AISI 304) with weld depths up to 15 mm. For two different amplitudes (3 and 6 μm) and three different positions of the weld pool in the vibration distribution (antinode, centered and node position) the weld metal is evaluated with metallographic cross sections. The types and the amount of microstructures are analyzed. The solidification of the weld metal is influenced by the vibration. Thus, the orientation, size and growth of the grains as well as the growth direction are changed. Furthermore, the weld characteristics (weld depth, weld width, weld area) are compared to the previously considered aspects.