Mn-doped and Mn–Al co-doped zinc oxide (ZnO) thin films were deposited on glass substrates by RF magnetron sputtering at room temperature. The X-ray diffraction results revealed that both films consisted of a single phase and had a wurtzite structure with a c-axis orientation. The electrical properties, transmittance characteristics, surface properties, and crystal structures of the films were investigated following annealing at temperatures ranging from 200 to 500 °C. The results showed that the as-deposited Mn:ZnO thin film had an average transmittance of 83%. The transmittance increased to 85% following annealing at 500 °C. The as-deposited Mn–Al co-doped ZnO thin film had a low transmittance of only 40%. However, after annealing at 500 °C, the transmittance increased to 83%. The annealed Mn–Al:ZnO thin film also showed a low electrical resistivity of 1.75 × 10−3 Ω·cm, an electron mobility of 20.8 cm2V−1s−1, and a carrier concentration of 5.3 × 1020 cm−3. Scanning electron microscopy (SEM) results showed that the crystal size of both thin films increased following annealing. Owing to their good optical and electrical properties, the annealed Mn–Al:ZnO thin films can be used as photosensor materials.