Powder mixing is an essential operation in pharmaceutical, food, and petrochemical industries. Pharmaceutical companies have been working in the implementation of continuous processes as an alternative to the batch process using the food and drug administration process analytical technology initiative. The main goal was to understand the mixing phenomena inside the continuous tumble mixer and monitor blend uniformity using discrete element method. Results demonstrated that the main mixing mechanism is convection similar to the common tumbling mixers. This mechanism is driven by the bulk flow of the particles, due to the mixer rotation. The simulations' results, demonstrated that the cohesion reduces the concentration variability due to the higher holdup, particle interactions, and mean residence time. The blend uniformity at the exit of the system was measured and a relationship between relative standard distribution, cohesion, and the collision frequency was found. (c) 2014 American Institute of Chemical Engineers AIChE J, 61: 792-801, 2015