The effect of grain size of a starting powder and heat treatment on thermoelectric efficiency (Z) of extruded samples of Bi_0,5Sb_1,5Te₃ and Bi₂Те_2,7Se_0,3 solid solutions in temperature range from 77 up to 350 K. It is clarified, that in case of Bi_0,5Sb_1,5Te₃ solid solution maximal Z is observed in samples with of grains 630 microns and passed heat treatment in vacuum at 690 K within 5 hours. In a case of Bi₂Те_2,7Se_0,3 solid solutions in samples with dimension of grans 630 microns, non-passed heat treatment. It is shown, that the obtained results are satisfactorily explained by effect of texture and structural imperfections on density and mobility of charge carriers, and also on the scattering mechanism of phonons in extruded samples of the investigated solid solutions.