Vetiver grass was used as an alternative filler in polypropylene (PP) composites in this study. Chemical treatment of vetiver grass by alkalization was carried out to obtain alkali-treated vetiver grass. It was shown that alkali-treated vetiver grass exhibited higher thermal stability than untreated vetiver grass. Injection molding was used to prepare the composites. The microstructure of injection molded samples showed a distinct skin layer due to shear-induced crystallization. It was found that normalized thickness of shear-induced crystallization layer of the composite was lower than that of neat PP. The effect of vetiver particle sizes on shear-induced crystallization and physical properties of the composites were elucidated. Furthermore, the effect of processing conditions on shear-induced crystallization, degree of crystallinity, gapwise crystallinity distribution, and mechanical properties of the composite were investigated. It was shown that injection speed and mold temperature affected the normalized thickness of shear-induced crystallization layer and degree of crystallinity of the composites. However, processing conditions showed insignificant effect on the mechanical properties of vetiver fiber-PP composites. The degree of crystallinity showed no distribution throughout the thickness direction of the composites. (C) 2009 Wiley Periodicals, Inc. J Appl Polym Sci 113: 4003-4014, 2009