Ultrasonic welding is a widely used joining method for joining individual components. Special features are local heating of the joining partners, short welding times as well as a high economic efficiency of the process. The weld seam quality depends on numerous factors. The welding process is affected intentionally and unintentionally, starting from the process parameters, the tolerances of the welding parts up to theories about a chaotic material model. This can lead to varying process qualities. Up to now, the weld seam quality is evaluated only by means of a destructive inspection of the weld seam. The sensory monitoring of the ultrasonic welding process provides information about the weld seam quality within the welding process. Within the scope of this work, the sensory monitoring of the mechanical vibrations occurring in the anvil as well as the temperature development in the joining zone of the weld seam are shown. From characteristic values for the sensory monitoring, a comparison is made between the weld seam quality from following tensile tests. The tensile strengths measured and the energy densities acquired at the piezo oscillator behave similarly.