The thermal conductivity as function of temperature and pressure is an important material property of polymers. Thermal conductivity is one of the important parameter in problems involving steady state heat transfer. However in injection molding simula¬tion the influence of pressure is mostly not considered. The aim of this study was to investigate the thermal conductivity of two different thermoplastic nanocomposites as function of temperature, nanofiller content and processing conditions based on acrylonitrile butadiene styrene (ABS) and additional as function of pressure on polypropylene (PP). The used nanofiller was layered silicates montmorillonite (MMT). For the production of PP nano¬composites (PPNCs) also compatibilizer (polypropylene grafted with maleic anhydride) was used. The measurements were carried out on high pressure capillary rheometer using a transient line-source method according to ASTM D5930-09. The thermal conductivity of ABS nanocomposites (ABSNCs) was measured at atmos¬pheric pressure as function of temperature, nanofiller content and screw speed. ABSNCs with three different nanofiller grades (2 wt.%, 3.5 wt.% and 5 wt.%) were produced using a co-rotating twin-screw extruder at two different screw speeds 100 min-1 and 300 min-1. An addition of 5 % layered silicates MMT lead to an increase in thermal conductivity by approximately 7.5 % for a screw speed of 100 min-1. Higher screw speed lead to a higher increase of thermal conductivity due to the better exfoliation of nanofiller in the polymer matrix up to 9.5 %. Thermal conductivity measurements as function of pressure, temperature, processing conditions and nanofiller content were carried out for PP and polypropylene nano¬composites (PPNCs) in melt and solid state. The pressure range reached from atmos¬pheric pressure to 750 bar for two different nanofillers content (5 wt.% and 10 wt.%) at different processing conditions. The PPNCs were produced with two different processing methods. On the one hand with the conventional underwater granulation process (UWG) and on the other hand with the use of an injection molding compounder (IMC). Two different types of formulations were produced and investigated. The first one was 3 in 1 which is a one-step-process in which PP, nanofiller and compatibilizer were compounded simultaneously. The second one was the master batch pre-stage process (MB). It is a two-step-process in which 50 wt.% of nanofiller and 50 wt.% of compatibilizer were compounded and pelletized. Afterwards the master batch was diluted with virgin PP to get the desired mixture. The effect of pressure lead to a significant increase in thermal conductivity for PP and PPNCs produced with the UWG. An approximately increase in thermal conductivity of 12 - 14 % was achieved in the melt state from atmospheric pressure to 750 bar. In the solid state the increase was even higher with approximately 19 - 28 % increase of the thermal conductivity. The results of the production with the IMC were slightly higher. The higher nanofiller content in PPNCs exhibited an increase in thermal conductivity in melt and solid state for both the process UWG and IMC. With the addition of 10 wt.% nanofiller the thermal conductivity increased approximately 10 % and the increase was approximately two times higher for the MB process compared with the 3 in 1 formulation for both the process UWG and IMC. These results were due to higher degree of dispersion and better exfoliation of the nanofiller in the polymer matrix.