Ultrasonic welding of plastic is state-of the-art technology. The thermal rise in the bonding area is produced by absorption of vibrations introduced. In the contraction area, frictional heat is produced so that material plasticizes locally, forging an insoluble connection between both parts within a very short period of time. The prerequisite is that both working pieces have a near equivalent melting point. To be able to extend the known influences and limits due to ultrasonic welding of plastic and metal parts the bonding process is of interest. In this study, the author applied the ultrasonic welding method to polyamide and polycarbonate plates and investigated the temperature distribution of the weld and the resulting flexural behaviour without the consideration of an optimum joint geometry.