Interest in the use of microalgae as a feedstock for biofuel production is primarily as a result of the capacity of some microalgae to accumulate lipids suitable for lipid-based biofuel production, such as biodiesel and hydrocarbons. Although biodiesel production is the most extensively studied process, the cost associated with oil extraction remains high due to the overall complexity of the procedure. To increase the efficiency of biodiesel production, it is necessary to consider the process as a global biorefinery concept, researching and integrating new production processes that will produce diversified products of higher added value. An alternative to the traditional production of biodiesel is the direct transesterification of microalgal biomass. The objective of this work was to use residual microalgae biomass (RMB) obtained from the production of biodiesel as a filler for compostable biocomposites. The microalgae used in this work, Nannochloropsis gaditana, were cultivated by Desert Bioenergy S.A. in the Microbial Ecology Laboratory of the University of Antofagasta in Antofagasta, Chile. The RMB was obtained after transesterification of the microalgae biomass. The chemical characterization of microalgae biomass and RMB was determined through a proximate analysis. The protein content in microalgal biomass and RMB was 23% and 42%, respectively. The bioplastic used for biocomposite production was poly(butylene adipate-co-terephtalate) (PBAT). The compositions of the composites were fixed at PBAT/RMB (90/10; 80/20; 70/30). For biocomposites pre-treated with silane and glycerol, the weight ratio of dry RMB was 20% to compare the effect with PBAT/RMB (80/20). All composites were characterized for thermal and mechanical properties.