β-Zn 4 Sb 3 is a cheap nontoxic high-performance thermoelectric material, which unfortunately suffers from stability issues because of zinc migration in thermal and electrical gradients.Here, the thermoelectric properties and thermal stability of β-Zn 4 Sb 3 mixed with varying sizes and weight percentages of TiO 2 nanoparticles are investigated. Furthermore, the stability of pressed β-Zn 4 Sb 3 -TiO 2 nanocomposite pellets is investigated by measuring high-energy synchrotron powder X-ray diffraction (PXRD) data during operating conditions using the Aarhus thermoelectric operando setup (ATOS). Through these studies, it is determined that TiO 2 nanoparticle addition in pressed pellets of β-Zn 4 Sb 3 does not prevent Zn migration, and even though effects are seen in the thermal conductivity and electrical resistivity, the overall zT remains unchanged regardless of TiO 2 nanoinclusions. For the present samples, the Seebeck coefficients are unaffected by the addition of nanoparticles, and thus, there is no observed energy-filtering effect. The operando PXRD data reveal that the TiO 2 nanoinclusions lower the degradation rate by up to 75%, but all samples eventually decompose. This is corroborated by long-term stability tests performed using a thermal gradient. In conclusion, TiO 2 nanoinclusions do not degrade the excellent thermoelectric properties of β-Zn 4 Sb 3 , but the stabilizing effect is not sufficient for establishing long-term operating stability.