<p>Size, size distribution and dispersibility are key parameters for silver nanoparticles (AgNPs), however, these properties are very difficult to control and to set precisely, especially in sustainable products and in a green and economical way. This study developed a facile, efficient, green and economical one-pot strategy to prepare AgNPs in a highly reproducible way with extremely small size, excellently narrow size distribution and high dispersion stability, by utilizing the glucurono-dialdehyde xylan (GlcU-DAX). GlcU-DAX played a bifunctional role, first as a reductant based on its (masked) aldehyde group content, and second as dispersing stabilizer for the formed AgNPs based on its carboxylic acid group content. Accordingly, the optimal formation conditions for AgNPs were elaborated, by which 99.7% of the formed AgNPs were spherical in shape with sizes below 10&#xa0;nm and a uniform dispersion. The compositional heterogeneity of glucurono-xylan, so far rather seen as hindrance for obtaining defined derivatives, was turned into a distinct advantage as both functionalities, the introduced aldehyde groups and the genuine carboxylic acids are needed to obtain the optimized AgNPs properties. The study thus also provided a new option for the high-value utilization of glucurono-xylan as biomass resource.</p>