An experimental study on ultrasonic welding of thermoplastic, which is a prelude to study how the technology can be adapted to join composite materials, was conducted. Three sets of specimen were studied to investigate the influence of energy guide on the bonded specimen. No major statistical difference between the ‘energy guides’ of the tested thermoplastic Celuka™ coupons were noted. Failure of the welded specimen was by shear at the interface. A 75% drop in strength for the bonded material was observed.