The　effect　of　warm-mix　additive　(WMA)　on　styrene-butadiene-styrene　(SBS)-based　high-viscosity　asphalt　(HVA)　was　conducted　in　this　study.　First,　the　physical　properties　for　control　HVA　and　HVA　with　WMA　(RH,　EC-120,　and　Sasobit　with　2%,　3%,　and　4%,　respectively)　were　evaluated　to　select　the　optimum　WMA.　Physical　tests　showed　that　all　WMAs　reduced　viscosity　(135°C)　significantly,　while　absolute　viscosity　(60°C)　was　improved　by　EC-120　and　Sasobit.　In　addition,　EC-120　improved　toughness　and　tenacity.　The　rheology　and　morphology　of　HVA　with　and　without　optimum　WMA　(3%　EC-120)　were　tested　using　dynamic　shear　rheometer　(DSR),　bending　beam　rheometer　(BBR),　and　scanning　electron　microscope　(SEM).　The　results　indicated　that　the　high-temperature　rheological　performance　was　improved　by　adding　EC-120　under　unaged　and　short-　and　long-term　aging　conditions.　In　addition,　EC-120　improved　the　low-temperature　creep　behavior　of　the　asphalt　binder　after　long-term　aging.　This　finding　was　further　demonstrated　by　morphological　observation,　in　which　a　multinetwork　was　formed　after　long-term　aging.　©　2018　American　Society　of　Civil　Engineers.