Protein-based thermoplastics offer an attractive alternative to petroleum-based plastics if their properties allow for large volume production using processes such as injection molding. A fractional factorial design was used to analyze the influence of injection-molding parameters (melt temperature, tool temperature, injection rate, holding pressure, and cooling time) on the injection-molding process (maximum injection pressure, injection pressure curve) and mechanical properties (tensile strength, elongation at break, secant modulus) of blood meal–based thermoplastics. Optimal mechanical properties were obtained at higher tool and melt temperatures while the injection rate was unimportant. The most important injection parameter was the holding pressure, which has to be lowered when using a higher melt temperature, which was preferred for better elongation at break. A lower holding pressure also produced moldings with a higher modulus, which could be good for demolding. Blood meal–based thermoplastics behaved mostly like standard thermoplastics, without any significant deviations. Within a workable processing window, its mechanical properties were largely unaffected by processing conditions, but as with any thermoplastic, care must be taken to select the best injection-molding parameter settings to achieve optimal part quality and high processability.