Thermoelectric materials are able to convert the thermal gradient ΔT into the voltage difference ΔV by the thermoelectric Seebeck effect and its associated coefficient S= -( ∆V)/( ∆T). To optimize the efficiency of thermoelectric materials, it is necessary to maximize the dimensionless figure of merit ZT=(σS^2)/κ T, where σ is the electrical conductivity, �� is the thermal conductivity, S is the Seebeck coefficient, and T is the temperature. Therefore, thermoelectric materials must exhibit a high electrical conductivity, a high Seebeck coefficient, and a low thermal conductivity1. Within this framework, semiconducting materials are the best thermoelectrics. Actually, thermoelectric commercial generators involve inorganic semiconductors which are often not environmentally friendly and scarce. An alternative is to use organic thermoelectric materials, either intrinsically conducting polymers or polymers filled with conductive nanoparticles for low temperature waste heat harvesting applications (T<500K)2,3. In this context, nanocomposites based on Poly(lactic acid) (PLA) filled with different percentages of carbon nanotubes (CNTs) were prepared to investigate their thermoelectric response at room temperature with a specific attention on the influence of elaboration process on the composite properties. For this, an amorphous and a semi-crystalline grade PLA, and multi-walled carbon nanotubes have been chosen. Extrusion or solution mixing, followed by hot-pressing were used to prepared thick PLA/CNTs samples (typically about 500 µm in thick). Differential Scanning Calorimetry (DSC) and X-Ray scattering results have shown that both grades of PLA are amorphous in all composites whatever the elaboration process used. Regarding the thermoelectric properties, as expected, the addition of CNTs significantly improves electrical conductivity by several orders of magnitude as soon as the CNTs fraction is higher than the percolation threshold (below 2 wt% CNTs). The higher value for the electrical conductivity in this study was around 102 S/m with 10 wt% CNTs. Note that the in-plane electrical conductivity of all PLA/CNTs appears 10-100 higher than values from cross-plan whatever the elaboration process used. By contrast, thermal conductivity is contained and slowly increases with the addition of CNTs: �� increases from around 0.20 for pristine PLA to 0.40 W/m.K with 10 wt% CNTs. Finally, the Seebeck coefficient is ranging from 10 to 12 µV.K-1 and does not seem to be dependent on the elaboration process either. These results evidence the strong anisotropy of thermoelectric properties on thick samples and the interest of further thin films investigations. References [1] C. Gayner, K.K. Kar Progress in Materials Science, 2016, Vol 83, 330–382. [2] Z. Antar, J. F. Feller, H. Noel, P. Glouannec, K. Elleuch Materials Letters, 2012, Vol 67, 210-214. [3] J. F. Brun, C. Binet, J. F.Tahon, A. Addad, P. Tranchard, S. Barrau Synthetic Metals, 2020, Vol 269, 116525.