Oil palm empty fruit bunch (EFB)-filled polypropylene (PP) composites were produced. The EFB filler was chemically modified with maleic anhydride (MAH). The effects of the filler size and chemical modification of EFBs on the tensile and dimensional stability properties of EFB-PP composites were studied. The composites with MAH-treated EFBs showed higher tensile strengths than those with untreated EFBs. This was attributed to the enhanced compatibility between the MAH-treated EFBs and PP matrix, as shown in a scanning electron microscopy study. Fourier transform infrared analysis showed evidence of C==C and C==O bonds from MAH at 1630 and 1730 cm(-1), respectively. The MAH-treated PP composites showed lower water absorption and thickness swelling than those with untreated EFBs.