Natural fibers have been thoroughly investigated in polymer composites area since many years ago. The main application of natural fibers has been as mechanical reinforcement. However, in the last decade the researches have been focus on new applications, such as flame retardant materials. In this work keratin and coconut fibers, recovered from Mexican industries wastes were investigated as multifunctional agents: mechanical reinforcement and flame retardants. A specific treatment was applied to fibers in order to obtain biopolymer composites base on biodegradable thermoplastic starch. The biocomposites were obtained by extrusion process. The effect of keratin and coconut fiber content and the joint action of fibers in combination with ammonium polyphosphate as fire retardant for biodegradable thermoplastic starch was studied by thermogravimetric analyses, UL94 classification, forced flaming combustion, mechanical and rheological analysis. It was found that when keratin or coconut fibers are added in combination with ammonium polyphosphate additive to biodegradable thermoplastic starch a synergistic effect leads to replace part of ammonium polyphosphate using 20% of keratin or coconut fibers. Keratin fibers and ammonium polyphosphate showed the same flame retardant properties. Coconut fibers and ammonium polyphosphate exhibited lower heat release rate than only ammonium polyphosphate at high content (20%). According to rheological measurements, flow behavior depends on the composition of biocomposites, Complex viscosity increases when keratin fibers are added in combination with ammonium polyphosphate with respect to biocomposites using high fiber content. Nevertheless, the combination of coconut fibers with ammonium polyphosphate showed a decrease on complex viscosity favoring the processing of these materials. This finding represents a promising alternative to produce ecological flame retardants and to reduce high waste from the Mexican industry