Conventional thermoelectric materials such as Bi2Te3 have the best performances at room temperature and can reach a ZT about 1. However, the cost, the toxicity and the scarcity of Te limit the application of thermoelectric materials in the low temperature range (300 – 600K). The use of eco-friendly elements such as silicides alloys could overcome these concerns. Among them Mn-Si and Mg2(Si,Sn) reached a maximum figure of merit of 0.63 (723 K) and 0.8 (650 K) respectively [1,2] and α-SrSi2 reaches a ZT about 0.15 at 300K which is the highest value for a silicide alloy at this temperature. The power factor of α-SrSi2 is close to that of Bi2Te3 however its thermal conductivity (~5 W/m.K) limit its performances. In this work, we investigate the effect of the nanostructuring, Sr purity and substitution on the thermal and thermoelectric properties of α-SrSi2 combining different metallurgical techniques [3,4]. We have shown that the nanostructuring by ball milling leads to an increase of the unit cell and of the concentration of defects which both modify the electronic band structure and phonon scattering. With this approach the lattice thermal conductivity contribution was decreased close to that expected to highly disordered or amorphous materials without impacting much the power factor. This multiscale approach enabled to improve the figure of merit to about 60% compared to our bulk reference. [1]Y. Sadia, L. Dinnerman, Y. Gelbstein, Mechanical alloying and spark plasma sintering of higher manganese silicides for thermoelectric applications, J Electron Mater. 42 (2013) [2]G. Jiang, J. He, T. Zhu, C. Fu, X. Liu, L. Hu, X. Zhao, High performance Mg2(Si,Sn) solid solutions: A point defect chemistry approach to enhancing thermoelectric properties, Adv Funct Mater. 24 (2014) [3]R. Ghannam, A. Moll, D. Bérardan, L. Coulomb, A. Vieira-E-Silva, B. Villeroy, R. Viennois, Mickaël Beaudhuin, Impact of the nanostructuring on the thermal and thermoelectric properties of α-SrSi2, J Alloys Compound 968 (2023) 171876 [4]R. Ghannam, L. Coulomb, A. Moll, D. Bérardan, A. Vieira-E-Silva, B. Villeroy, R. Viennois, Mickaël Beaudhuin, Enhanced thermoelectric properties of p-type α-SrSi2 nanostructured by melt spinning, J. solid state sci 147 (2024) 107406