Due to their good specific weight related mechanical properties fiber reinforced plastics are a popular material with rising demand especially in lightweight applications. In order to recycle fiber reinforced end-of-life products, the mechanical recycling process represents a sustainable solution for thermoplastic composites as they can be easily shredded, melded and processed into new applications. One challenge is the fiber dust formation during shredding of fiber reinforced scrap, as the fiber dust disturbs the production process and poses a potential health risk. The arising fibers can be alveolar and thus potentially toxic. Therefore, it is a main goal of this research to investigate the influence of different fiber contents and lengths of thermoplastic composite materials on the fiber dust formation during shredding, with the purpose to identify material specific shredding parameters which have an influence on fiber dust formation. The aim is to adjust these parameters so that the fiber dust formation is reduced. Polyamid -6 and Polypropylen with different amount of short glass fiber as well as with continuous glass fiber fabric reinforcement and Polyamid-66 with short carbon fibers and continuous carbon fiber fabric reinforcement where shredded using a cutting mill. Results show that shredding of organic sheets creates most fiber dust and finest particles compared to short fibers. A slight effect can be seen with increasing fiber content for short fiber reinforced materials. A reduction of rotational speed during the shredding process further reduces the amount of fiber dust for all materials whereas the effect on the fiber length distribution is neglectable. For carbon fibers the material with the highest content of small particles in the ground material after sieving also provides the shortest fibers in the fiber length distribution. For glass fibers reinforced materials the content of fine fiber dust depends on the matrix material.