This invention relates to a thermoelectric material constituted of nanostructures and a thermoelectric element and an optical sensor including the same, as well as to a method for manufacturing a thermoelectric material constituted of nanostructures. An object of the present disclosure is to achieve better thermoelectric characteristics of the thermoelectric material containing nanoparticles. The thermoelectric material includes a first material having a band gap and a second material different from the first material. The thermoelectric material contains a plurality of nanoparticles distributed in a base material which is a mixture of the first material and the second material. A composition of the second material in the thermoelectric material is not lower than 0.01 atomic % and not higher than 2.0 atomic % of the thermoelectric material.