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As an important ecofriendly material in pavement engineering, bioasphalt has received more and more attention recently. However, the negative high-temperature behavior of bioasphalt limits its extensive application. With the purpose of enhancing the bioasphalt high-temperature behavior, polyphosphoric acid (PPA) was used to modify bioasphalt. The PPA/bio-oil composite–modified asphalt's high-temperature behavior was investigated by the dynamic shear rheometer (DSR) test. The low-temperature behavior was evaluated by using the bending beam rheometer (BBR) test. Finally, the modification mechanism of modified asphalt was analyzed by carrying out a Fourier-transform infrared reflection (FTIR) test. The results indicated that compared with the neat asphalt, the rutting index of PPA/bio-oil composite–modified asphalt was significantly improved. Also, it had excellent low-temperature crack resistance. As the bio-oil and PPA contents in respect to the weight of neat asphalt were 15% and 5%, respectively, PPA/bio-oil composite–modified asphalt performance was optimal. Shear time and shear rate did not have a remarkable effect on PPA/bio-oil composite–modified asphalt performance. Moreover, bio-oil did not affect the chemical structure of the neat asphalt. But, PPA generated new chemical functional groups with neat asphalt and produced chemical modification. This research makes pavement engineering greener, more economical, and environmentally friendly. [ABSTRACT FROM AUTHOR]