This paper reports an improved headspace gas chromatography (HS-GC) technique for the determination of carboxyl group content in wood fibers. The method is based on phase reaction conversion HS-GC technique developed previously [Chai et al., Ind. Eng. Chem. Res. 2003, 42, 5440-5444], but with major modifications in regard to sample preparation (i.e., sample acidification followed by water washing), reaction reagent concentration (i.e., minimization of bicarbonate decomposition), and the manner for sample addition (i.e., a direct sample addition). As a result, this technique greatly improves the measurement precision. The present method is simpler, more reliable, and more practical. It can be applied to the nonfiber samples.