Natural fibers (NFs) are rich in cellulose and also they are a low cost, easily renewable source for polymer composites. However, the presence of impurities (waxes, lignin, etc.) and hydroxyl groups produce those NFs with less ability to reinforce polymeric matrices. Short sisal fibers (SSF) were subjected to three different chemical treatments (alkaline, dicumyl peroxide, and silane). Composites of ethylene vinyl acetate (EVA) and chemically modified SSF were prepared by mechanical mixing at the melt state of the polymer matrix (130 degrees C) using a two roll mill. The influences of fiber content and chemical treatment on the mechanical properties of the composites were evaluated. The tensile strength increased for every such treated SSF-reinforced composite. There was also a noticeable increase in elastic modulus compared with the unfilled matrix. The elongation at break values decreased as the fiber content was increased. Moreover, it was observed that the surface treatment of the SSF improved the fiber dispersion within the EVA matrix. The thermal stability of SSF was analyzed by thermogravimetic analysis. Potentially, the recyclability of the composites might be promising due to the lower specific gravity of NF, accompanied by low cost, and with the added advantage of biodegradability. POLYM. ENG. SCI., 2013. (c) 2012 Society of Plastics Engineers