In this work, improvements in the photosensitivity of undoped POFs, where there was a well-defined pre-annealing of the preform, were reported. We have noticed that with non-annealed preforms, the fiber photosensitivity is lower. The fibers from preforms with specific thermal pre-treatment allow us to achieve less FBG inscription times than fibers with no well-defined annealing, obtaining at the same time stable FBG sensors with high quality. We also addressed the actual influence of annealing on the strain sensitivity of the fibers prior and after FBG inscription, showing that the fiber produced from a preform with well-defined pre-annealing did not produce any significant difference. Some important parameters were considered such as drawing tension and water content, where using fibers drawn in different tensions give us a similar FBG inscription time. We can also conclude that a fiber drawn from a preform which had not a specific process of annealing, it will include a slight amount of water inside of preform and will affects the fiber performance.