Blue phosphorene is an attractive nanomaterial that exhibits some remarkable optoelectronic properties. Various studies have verified its ability to adsorb gaseous compounds and, in particular, to dissociate O 2 , forming covalent bonds between phosphorus and oxygen atoms. These covalent bonds could be the reason behind the oxidation reaction that affects the blue phosphorene in normal room conditions. Theoretically, it has been demonstrated that the blue phosphorene oxide (BPO) is just as stable as the blue phosphorene. Given that metallic oxides are widely used as catalyzers and gas sensors, this opens the possibility of the BPO being presented as a gas sensor as well. For all the above, in this work the optoelectronic properties of BPO were studied, along with the generation of the oxygen vacancies. The investigation was performed within the density functional theory (DFT). In the study of the oxygen vacancy, the formation energy was calculated, and the results are similar to the formation energies of oxygen vacancies in other known oxides. It was found that the BPO with a single vacancy has a favorable energetic stability. The characterization of the vacancy is achieved using the electronic structure and the optical response. Additionally, the analysis of the adsorption of a hydrogen atom on the BPO, and the subsequent formation of hydroxide is presented.Blue Phosphorene Oxide, DFT, oxygen vacancies, phosphorene 1 | INTRODUCTION Two-dimensional materials have become popular in the past decade as possible candidates for the development of applications in optoelectronics and gas-sensor manufacturing. Due in part to monolayer's unique electronic properties, in particular, its high surface/volume ratio. It is also possible to manipulate the electronic properties in these materials using functionalization, whether it is by doping, the presence of structural defects, or by creating heterostructures that combine monolayers of different chemical compositions. [1][2][3][4][5][6][7][8][9][10][11][12] Phosphorene is one of those materials that show attractive electronic features. Several theoretical studies have been conducted to evaluate the possible applications of its monolayer form as well as the realization of multilayered structures based on it. For instance, recent studies on this material have shown that it is, in fact, a nanosystem with an electronic bandgap, which can be controlled by modifying the number of layers. [13] In this sense, phosphorene becomes a promising nanosystem due, in the first place, to its physical-chemical properties and, secondly, for the challenge that poses maintaining its structural stability at room conditions, since it has revealed itself as a highly reactive material. Thus, interactions with some gases might induce significant changes in its electronic structure.