The effect of temperature, humidity and incident UV light on the photocatalytic activity of two TiO2 films with different microstructures (dense and mesoporous) was explored in terms of stearic acid degradation. Previous works reported in the literature suggest that the activity of TiO2 films does not only depend on single factors but also on interactions between them. Hence, the design of experiments (DoE) approach was used in this work to plan the experiments in a systematic way, simultaneously considering several variables. This approach provided an efficient working strategy to explore both individual and interaction effects on the photocatalytic activity of the films. The statistical evidence found here revealed that single factors temperature and mesoporous microstructure have the strongest positive effect on the efficiency of the films. In the case of temperature, this was explained by easier degradation and/or desorption of reaction intermediates. On the other hand, the positive effect of the mesoporous microstructure was correlated with its large surface area. An interaction factor between temperature and incident UV light also affects the activity of the films. Results suggest that this phenomenon depends of the degree of film hydration before the deposition of SA. (C) 2016 Elsevier B.V. All rights reserved.