High-elastic　modified　(HEM)　asphalt　was　prepared　by　the　addition　of　styrene-butadiene-styrene　(SBS),　plasticizer,　and　crosslinker　to　base　asphalt.　The　effect　and　proportion　of　each　modifier　in　asphalt　were　studied　using　physical　and　rheological　tests.　It　was　found　that　SBS　determined　the　high-temperature　performance　of　HEM　asphalt　mainly.　Plasticizer　(dioctyl　phthalate)　is　very　helpful　in　improving　the　low-temperature　flexibility　and　elastic　recovery.　Crosslinker　(sulfur)　is　necessary　in　maintaining　high-temperature　stability.　In　this　study,　Fourier　transform　infrared,　hydrogen　nuclear　magnetic　resonance　analysis,　and　microscopy　observation　were　used　to　investigate　the　structural　characteristics　of　modified　asphalts　further　before　and　after　ageing.　The　research　showed　the　structural　characteristics　of　modified　asphalt　were　influenced　evidently　by　ageing.　©　2015　Wiley　Periodicals,　Inc.