A non-isothermal crystallization study on two different 30%w carbon fiber (PAN and pitch-based) reinforced PEEK was performed by differential scanning calorimetry (DSC), aiming to provide more information on PEEK crystallization behavior in the presence of reinforcements. Melt crystallization was performed by cooling down the CFR-PEEK samples from the molten state with different cooling rates (from 2 to 50 degrees C/min). Samples were subsequently heated up again at 400 degrees C at 20 degrees C/min to evaluate any potential differentiation in the created crystal structures. The same experiments were run also for unfilled PEEK, taken as reference. Crystallization kinetics (with Avrami and Avrami-Ozawa approaches), and activation energies (according to Friedman method) were evaluated. The results showed that the cooling rate influences crystal growth and morphology but also, more importantly, that fiber type affects the crystallization mechanisms, either favoring or hindering polymer crystallization, depending on the fiber characteristics, geometry and density. Overall, these observations suggest that accurate fiber selection and processing conditions set up have to be chosen to ensure an optimal polymer morphology. (C) 2016 Elsevier B.V. All rights reserved.