A novel flow improver, the copolymer of octadecyl acrylate, styrene, and maleic anhydride (OASA), was prepared by copolymerization and esterification reaction to study its viscosity-reducing effect on bitumen based its existing application on crude oil. In this paper, chemical compositions, thermal stability, and viscosity were characterized by infrared spectra (IR), differential scanning calorimetry (DSC), and Brookfield Viscometer, respectively. Besides, conventional properties of modified bitumen were investigated to study the effect of modifier. Results shown that OASA modification was physical and its mechanism was the combination effect of polar moiety and long alkyl chain of OASA copolymer; thermal stability of modifier was good enough to capable for asphalt mixing and compaction; viscosityreducing effect of OASA was proved with a considerable range and the effect was negative to temperature increasing; as for bitumen conventional properties, penetration and ductility got increased while the softening point got decreased under the OASA modifying effect. (C) 2016 Elsevier Ltd. All rights reserved.