Wood-plastic composites (WPCs) have been widely used as exterior construction materials. The effect of alkali-treated (with NaOH concentrations of 1%, 3%, 5%, and 7%) eucalyptus fiber on the three-body abrasion behaviors of eucalyptus/polyvinyl chloride (PVC) composites was investigated. The results showed that the eucalyptus fiber treated with NaOH had a higher crystallinity and improved hardness and impact strength. The wear loss and rate of alkali-treated eucalyptus/PVC composites was noticeably decreased compared to the natural eucalyptus fiber. The scanning electron microscopy (SEM) examination on the worn surfaces revealed that the main wear mechanism of the eucalyptus/PVC composites was a combination of microcutting and microindentations.