Untreated and alkali-treated fibers from tamarind fruits were analyzed with Fourier transform infrared, chemical, X-ray, and thermogravimetric methods. The morphology of the fibers before and after the alkali treatment was studied with scanning electron microscopy. The tensile properties of these fibers before and after the alkali treatment were also studied. The Fourier transform infrared and chemical analyses indicated lowering of the hemicellulose content by the alkali treatment of the fibers. The tensile modulus increased with the alkali treatment. X-ray diffraction revealed an increase in the crystallinity of the fibers with the alkali treatment. The thermal stability of the fibers increased slightly with the alkali treatment. (C) 2008 Wiley Periodicals, Inc.