There are some reports related to applications of ultraviolet (UV) and water to enhance the electrical performance of metal oxide thin-film transistors (TFTs). We recently discovered that treatment timing and treatment method are also important for a good metal oxide thin-film formation. There are different influences on the metal oxide TFTs' electrical properties based on the UV irradiation and water treatment timing. The field-effect mobility of TFTs treated with UV-irradiation and water, which was spin-coated on the UV-irradiated film after pre-annealing, increased to 4.71 cm²V-1s-1 and 6.41 cm²V-1s-1. This was higher than the 3.39 cm²V-1s-1 field-effect mobility of non-treated TFTs. On the other hands, TFTs which were fabricated by the same method, with only varying the treatment time, after post-annealing, exhibited the tendency to show a decrease in field-effect mobility to 1.93 cm²V-1s-1 and 1.32 cm²V-1s-1, gradually, showing a contrasting tendency with the former conditions.