Bismuth oxyiodide (BiOI) has received much attention in the design of materials, because this material has proved its potential application in heterogeneous photocatalysis for environmental decontamination processes using visible light or simulated solar radiation. In this study, standard conditions and a reproducible method of solvothermal synthesis are established in order to obtain BiOI microspheres with higher photocatalytic activity in the degradation of gallic acid. Standard conditions of reaction temperature and reaction time turn out to be 126 C and 18 h, respectively. In addition, results show that reaction temperature has a stronger influence on different properties of the BiOI, affecting the photocatalytic efficiency. BiOI materials were synthesized by solvothermal process using different ranges of reaction temperature (120–200 C) and reaction time (12–24 h). Eleven experiments were designed, applying response surface methodology. The morphological, optical, and chemical properties of the best and worst material were determined using several techniques.