In this study, thermoelectric properties of the two sided-closed single-walled boron nitride nanotubes (TSC-SWBNNTs) are investigated. For this purpose, a nanotube with the chirality of (6, 3) is selected with no impurities. The energy is considered in the range of -5.5 to 5.5 electron volts and the investigations are performed at the temperatures 300, 500, 700 and 900K. The results show that increasing temperature results in significant reduction in the length of the bandgap. Besides, the peaks of the conduction diagram become smaller and their number decreases, indicating the return of more electrons and holes around the LUMO and HOMO bands, respectively, which leads to reduction of the bandgap and increase in the conduction. Moreover, the seebeck coefficient (thermal power) has increased to about 370 μV/K by increasing temperature to 900K. As the temperature increases, the coefficient of merit (ZT) increases to about 0.95, and it is expected to experience more increase with further increase in temperature. Thermal conductivity has also increased slightly with increasing temperature. However, the values of thermal conductivity are at the nanoscale. Therefore, in general, it can be concluded that the (TSC-SWBNNT) (6, 3) can be selected as a suitable thermoelectric material.