Thermal degradation of grape seeds alone and mixed with polyethylene was studied by TG-MSD and by pyrolysis at 500 degrees C, followed by GC-MSD analysis of liquid products. The maximum degradation rate was found at 390 degrees C for grape seeds and at 475 degrees C for polyethylene. Interactions are possible between the two materials or their degradation products at co-pyrolysis, with an effect on product yield. The main components of pyrolysis oils from grape seeds are fatty acids, followed by lignin-derived compounds. Light carboxylic acids, homologous series of paraffins and olefins and benzene derivatives were also identified. The effect of Red Mud and FCC catalysts on the thermal behaviour and on the pyrolysis yield was tested in liquid and vapour phase contact mode. They enhanced the degradation and changed the product yield.