AbstractXylan is known as a strength-enhancing agent for paper. However, it is difficult to adsorb xylan onto cellulose fibers because it carries the same negative charge as fibers. Therefore, either cationization of xylan or addition of cationic polyelectrolyte is required to maximize the effect of xylan use. In this study, cationic polyelectrolyte was used to promote xylan adsorption onto cellulose fiber. The effect of the polyelectrolyte type on the successive adsorption of xylan and its influence on paper properties was examined. The mechanism for improving paper strength by xylan adsorption on polyelectrolyte pre-formed layers was investigated through the viscoelastic properties of the preformed layers on model cellulose films using Quartz Crystal Microbalance with Dissipation (QCM-D). Both tensile and tear indices of paper were improved with the adsorption of xylan onto pulp fibers. It was suggested that the adsorbed xylan onto the polyelectrolyte preformed layer formed a complex layer that gave rise to a large contact area between xylan and fiber. The increase in the physical strength of paper depended on the structure of the polyelectrolyte-xylan layers. Highly charged cationic polyelectrolytes that form a flat adsorption layer gave a relatively lower increase in physical properties. On the other hand, thicker and more viscous adsorbed layers improved paper strength significantly.