This work deals with the numerical and experimental investigation of droplets breakage in SMX+ static mixers. While steady-state empirical correlations are commonly used for the prediction of the mean droplets size (e.g. Sauter mean diameter) during emulsification in static mixers, in the present study, a population balance equation (PBE)-based model is developed for the prediction of the dynamic evolution of the droplet size distribution (DSD). The system silicon oil-in-water stabilized by Polysorbate 20 (Tween20 R) is considered under dilute conditions (< 5%vol.). Due to the physico-chemical properties of the system and the operating conditions, the droplets breakage process is dominant, while coalescence and Ostwald ripening are negligible. The breakage kernel proposed by Alopaeus et al. [1] is employed and its parameters are identified and validated for the present system under different operating conditions. The effects of the number of SMX+ elements, viscosity and fraction of the dispersed phase, the DSD at the inlet of the mixers as well as the volume-average energy dissipation rate within the SMX+ elements on the evolution of the DSD are investigated. The model was found to be able of predicting the DSD over a wide range of operating conditions.