Thermoelectrics are materials that can be used to convert heat directly into electricity via the thermoelectric Seebeck effect. 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, �� the thermal conductivity, S the Seebeck coefficient, and T 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. During the last decade, organic thermoelectrics have emerged as a relevant alternative to inorganics for low temperature waste heat harvesting applications (T<500 K) including carbon nanotubes/polymer based nanocomposites2,3. In this study, nanocomposites based on a Poly(lactic acid) (PLA) filled with different percentages of carbon nanotubes (CNTs) (up to 10 wt%) were prepared to investigate their thermoelectric properties at room temperature with a particular attention to the influence of elaboration process. For this, an amorphous and a semi-crystalline grade of PLA, and Multi-walled carbon nanotubes have been chosen. Extrusion or solution mixing, followed by hot-pressing process are being used to prepare 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 the composites whatever the elaboration process used. Regarding the thermoelectric properties, as expected, CNTs significantly improve electrical conductivity by several orders of magnitude as soon as the CNT fraction is higher than the percolation threshold (below 2 wt% CNT). The higher value for the electrical conductivity measured in this study was around 102 S/m with 10 wt% CNT. Note that the in-plane electrical conductivity of all PLA/CNTs appears 10-100 times higher than the values from cross-plane whatever the elaboration process used. By contrast, thermal conductivity is contained and slowly increases with the addition of CNT: �� increases from around 0.2 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. References [1] Gayner, C.; Kar, K. K. Recent advances in thermoelectric materials. Progress in Materials Science 2016, 83, 330–82. [2].Antar Z., Feller J. F., Noel H., Glouannec P., Elleuch K., Thermoelectric behaviour of melt processed carbon nanotube/graphite/poly(lactic acid) conductive biopolymer nanocomposites (CPC). Materials Letters 2012, 67, 210-214. [3] Brun, J. F. ; Binet, C. ; Tahon, J. F. ; et al. Thermoelectric properties of bulk multi-walled carbon nanotube - poly(vinylidene fluoride) nanocomposites: Study of the structure/property relationships. Synthetic Metals 2020, 269, 116525.