The polysaccharides in oil palm trunk fibre and empty fruit bunch (EFB) fibre were fractionated into cold water solubles, hot water solubles, 1% NaOH solubles, and 17.5% NaOH soluble fractions. Cellulose (approximately 42%) and hemicelluloses (approximately 33%) were the major polysaccharides in the palm trunk fibre and EFB fibre. Extractions of the lignified fibres with cold water, hot water, and 1% NaOH produced the hemicellulosic fractions, which were enriched in xylose and glucose and to a lesser extent, arabinose-, galactose-, mannose-, rhamnose-, and ribose-containing polysaccharides, together with noticeable amounts of associated lignin (4.5–31.2%). Further extraction of the delignified fibre residues with aqueous 17.5% NaOH removed the hemicellulosic fractions, which were strongly enriched in xylose-containing polysaccharides and relatively free of associated lignin (0.3–0.7%). Eight phenolic acids and aldehydes, including p-hydroxybenzoic acid, p-hydroxybenzaldehyde, vanillic acid, syringic acid, vanillin, syringaldehyde, p-coumaric acid, and ferulic acid, were detected in the mixtures of alkaline nitrobenzene oxidation of associated lignin in all the sixteen polysaccharide fractions. The results obtained showed that hemicelluloses in the cell walls of oil palm trunk and EFB fibres, are mainly bonded with lignin by syringyl units.