<p>Taiwan is surrounded by the sea, and harbor engineering projects are continuously being constructed and maintained. Additionally, coastal roads are long-term exposed to seawater and sea winds, which degrade the durability of asphalt concrete pavement. Therefore, this study aims to apply Basic Oxygen Furnace (BOF) slag to asphalt concrete and evaluate its effectiveness in enhancing the engineering properties through resilient modulus and creep tests. Furthermore, the study investigates the impact of freshwater and seawater on the moisture damage resistance of BOF slag asphalt concrete using boiling tests, immersion residual strength tests, and Cantabro loss tests. The research results indicate that BOF slag has a higher specific gravity and better abrasion and crushing resistance than natural aggregates. Long-term immersion in seawater promotes the formation of CaSiO₃ and MgSiO₃, stabilizing the volume of BOF slag. However, prolonged water immersion leads to a decrease in abrasion resistance, with an increase in wear rate of about 3–4.6%. The mechanical property tests, including resilient modulus, static creep, and dynamic creep tests, demonstrate that asphalt concrete containing BOF slag has better deformation resistance than asphalt concrete with natural aggregates. Additionally, BOF slag asphalt concrete effectively reduces the adverse effects of temperature variations during transportation. Moreover, the results of the boiling test, immersion residual strength test, and Cantabro loss test indicate that seawater causes more severe moisture-induced stripping damage to natural aggregate asphalt concrete than freshwater. However, the degree of stripping damage in BOF slag asphalt concrete is similar in both seawater and freshwater environments. Based on these findings, BOF slag can effectively enhance the engineering properties and moisture damage resistance of asphalt concrete, providing valuable insights for its application in harbor and coastal road engineering projects.</p>