The objective of this study was to carry out the surface treatment of agave fibers in a solution of maleic anhydride grafted to poly(lactic acid) (MAPLA) in order to prepare compatibilized biocomposites produced by rotational molding. Moreover, the effect of surface treatment on the physical and mechanical properties was evaluated at different fiber content (10, 20 and 30 wt.%). Fibers’ surface modification was confirmed by means of FTIR and SEM analyses indicating the presence of a polymer coating at the fibers’ surface. The treatment enhanced compatibility in the treated fiber biocomposites (TFC) as it was confirmed in SEM micrographs where no pull-out or debonded fibers were observed in contrast with untreated fiber composites (UFC), indicating that stress was effectively transferred through the interface. This ultimately led to enhance mechanical properties in comparison with UFC. For instance, tensile properties increased from 25 to 41 MPa and from 1.30 to 1.74 GPa for strength and modulus, respectively, when fiber content was set at 20 wt.%. Grafting PLA chains to the surface of the fibers resulted in decreasing fiber’s hydrophilicity since water absorption at equilibrium decreased by 39% at 20 wt.% of fiber content, whereas lower water diffusion coefficients were observed for the biocomposites, i.e., a decrease of 22% (1.30x10-8 to 1.01x10-8 m2/s) was observed at 30% of fiber content. However, at this fiber loading, the SEM micrographs showed that there was not enough polymer to fill the volume between the fibers and completely cover them, thus high porosity led to a substantial decrease in mechanical properties even for TFC.