The ZnO (99%) and Al (1%) powders were combined in a manual pellet press to form the ZnO:Al pellets, which were subsequently annealed in an oxygen atmosphere at temperatures ranging from 600 °C to 900 °C. X-ray diffraction data indicated improved crystallinity up to an annealing temperature of 700 °C because of the compensation of donor defects caused by oxygen vacancies. The quality of the crystal decreased because of further annealing, which caused oxygen atoms to diffuse into interstitial sites. The Seebeck measurements showed an increase in the values up to the annealing temperature of 700 °C, with a decrease at higher temperatures. The electrical conductivity showed a decreasing trend up to 700 °C, followed by an increase with further annealing. The observed behavior of the Seebeck coefficient and electrical conductivity with annealing temperature suggests enhanced carrier concentration and mobility. The significant improvement in thermoelectric properties can be attributed to the enhanced mobility of charge carriers.