The present master thesis addresses development, processing and characterization of natural fiber-reinforced, thermoplastic biopolymers (biocomposites). Matrix polymers were poly(butylene succinate) (PBS) as well as a polymer blend of polyhydroxyalkanoate and poly(butylene adipate-co-terephthalate) (PHA/PBAT). Fibers were flax, hemp, coir and sisal, which were used in the form of technical short fibers. In order to study the effect of surface treatment on fiber-matrix-bonding alkali treatment was applied additionally. For the preparation of biocomposites a methodology and the according processing techniques were developed and applied. These included the preparation of fiber/biopolymer-pellets and subsequent compounding of the polymer matrix with the pellets. Fiber concentration was varied between 10 and 30 vol%. Actual fiber concentration within the biocomposite was determined via thermogravimetric analysis (TGA) and was within ±10 % of the theoretical fiber volume fraction. As matrix and fibers thermally degrade almost simultaneously a specific methodology has been developed and applied to determine the fiber volume fraction from TGA measurements. Natural fibers affected crystallization kinetics, especially recrystallization of the polymers. Moreover, the degree of crystallinity was influenced. Mechanical characteristics were determined on specimens prepared from compression molded plates. Increasing fiber concentration yielded an increase in stiffness as well as a decrease in tensile strength and elongation at break. Moreover, impact strength was decreased with increasing fiber concentration. No distinct correlation between fiber surface treatment, fiber-matrix-bonding, and mechanical properties was established. However, the results show that surface treatment might enhance mechanical properties slightly. In terms of mechanical properties the developed biocomposites are not competitive to conventional thermoplastics, such as glass fiber composites (GFC), yet. Nevertheless, natural fiber reinforcement extends the applicability as well as the field of application of thermoplastic biopolymers.