Chemically synthesized ZnS thin film is found to be a good x-ray radiation sensor. We report the effect of annealing on the x-ray radiation detection sensitivity of a ZnS thin film synthesized by a chemical bath deposition technique.The chemically synthesized ZnS films are annealed at 333, 363 and 393 K for 1 h. Structural analyses show that the lattice defects in the films decrease with annealing. Further, the band gap is also found to decrease from3.38 to 3.21 eV after annealing at 393 K. Current-voltage characteristics of the films are studied under dark and x-ray irradiation conditions. Due to the decrease of lattice defects and band gap, the conductivity under dark conditions is found to increase from 2.06×10~(-6)to 1.69×10~(-5) S/cm, while that under x-ray irradiation increases from 4.13×10~(-5) to 5.28×10~(-5)S/cm. On the other hand, the x-ray radiation detection sensitivity of the films is found to decrease with annealing. This decrease of detection sensitivity is attributed to the decrease of the band gap as well as some structural and surface morphological changes occurring after annealing. Chemically synthesized ZnS thin film is found to be a good x-ray radiation sensor. We report the effect of annealing on the x-ray radiation detection sensitivity of a ZnS thin film synthesized by a chemical bath deposition technique. The chemically synthesized ZnS films are. Annealed at 333, 363 and 393 K for 1 h. Structural analyzes show that the lattice defects in the films decrease with annealing. Further, the band gap is also found to decrease from 3.38 to 3.21 eV after annealing at 393 K. Current- Due to the decrease of lattice defects and band gap, the conductivity under dark conditions was found to increase from 2.06 × 10 -6 to 1.69 × 10 -6. (-5) S / cm, while that under x-ray irradiation increases from 4.13 × 10 -5 to 5.28 × 10 -5 S / cm. On the other hand, the x-ray radiation detection sensitivity of the films is found to decrease with annealing. This decrease of detection sensitivity is attribute d to the decrease of the band gap as well as some structural and surface morphological changes occurring after annealing