This study is based on MgO thin films, on which different amounts of bismuth were doped. XRD, SEM and EDX were performed for the characterization of thin films, whereas capacitance of the films was examined through current-voltage measurements. In addition, capacitance of these films was measured in the environments with violet, green, red and yellow lighting. It was found that under violet light, in other words around the UV region, the capacitance of Bi-doped thin films increased by 15%. SEM and EDX analysis revealed that the percentage of bismuth on the surface was dramatically increased with the increase of doped bismuth amount. On the other hand, various differences were observed on the surface images of doped and undoped films, serious differentiations were especially observed on the morphologic structure of 15% Bi-doped films.