In this study, the interfacial adhesion between polyurethane (PU) resin and ultrahigh- molecular-weight polyethylene (UHMWPE) fiber, which was coated with low-concentration PU after plasma treatment, was investigated. First, the UHMWPE fiber was treated with nitrogen plasma. Subsequently, it was coated with extremely low-concentration PU resin for improving its interfacial adhesion with the PU resin. The effects of plasma treatment and low-concentration PU coating were analyzed using XPS, FTIR-ATR, SEM, and AFM. Furthermore, the interfacial shear strength between the plasma-treated UHMWPE fiber and PU resin was measured using the microdroplet test. Consequently, the interfacial adhesion was improved by the low-concentration PU coating after the plasma treatment, due to the increase in mechanical interlocking and molecular diffusion of PU resin.