In the following, the effect of heat conduction along carbon fibres within the frame of laser transmission welding process is investigated. Therefore the heat conduction in unidirectional continuous carbon fibre reinforced polyphenylene sulfide (CF PPS UD) was examined without and with a laser transparent partner. The experiments were performed with a Nd:YAG and a diode laser. For the evaluation, the temperature was monitored with a thermo camera and a pyrometer. Furthermore, optical micrographs of the weld seam were prepared to determine the weld seam shape depending on the fibre direction. Additionally, the influence of the welding technique, contour and quasi-simultaneous welding, on the weld seam width was determined.