Natural fibers have received the attention of researchers due to their ecological character, biodegradability, low costs, non-abrasive nature, high filling levels, low energy consumption, high specific properties, low density and wide variety of fiber types. However, the polar and hydrophilic nature of lignocellulosic fibers and the non-polar characteristics of most thermoplastics results in different levels of incompatibility and compounding difficulties leading to non-uniform fiber dispersion within polymer matrices, thus limiting their efficiency [1]. Therefore, it is necessary to use physical or chemical treatments to improve the fiber-matrix compatibility. In this study, agave (Agave tequilana Weber var. Azul) and coir (cocus nucifera) fibers were surface treated with maleated polyethylene (MAPE) with two main objectives: 1) to improve the mechanical properties of the composites produced by rotational molding, and 2) to increase the fiber content in the composite. The rotomolded composites were produced with linear medium density polyethylene (LMDPE) and different concentrations (0, 10, 20, 30 and 40% wt.) of fiber (treated or untreated). The samples were then characterized in terms of morphology and mechanical properties (impact, tensile and flexural). The results showed that the MAPE surface treatment was successful leading to a better fiber distribution and a more uniform composite morphology allowing the possibility to use higher fiber contents in rotational molding. At low fiber contents (10 and 20% wt.), the mechanical properties were improved (up to 52%) in treated fiber composites (TFC) compared to the neat polymer and untreated fiber composites (UFC). Although the mechanical properties of TFC decreased at high fiber contents (30 and 40% wt.), they were substantially higher than UFC (about 160%, 400% and 240% for impact, tensile and flexural properties, respectively). [1]. E.O. Cisneros-López et al., Polym. Compos. DOI: 10.1002/pc.23564 (2016) Figure 1. Relative (σcomposite/σLMDPE) tensile and flexural strength.