Abstract: The autoignition characteristics of different proportions of n-butanol/biodiesel blends were experimentally investigated on a newly developed ultrahigh pressure rapid compression machine at the equivalence ratio ranging from 0.3 to 1.0,the compressed pressure of 1—6 MPa and the compressed temperature ranging from 700 K to 975 K. The results show that the ignition delay time of the blended fuels drops with the increase of temperature,pressure and equivalence ratio,while increases with the increase of the proportion of n-butanol. However,the ignition delay time becomes insensitive to the blending ratios of n-butanol with the increase of temperature. Simulation studies were also carried out using the existing detailed kinetic models to compare with the experimental results.The chemical interaction between n-butanol and biodiesel during autoignition was investigated by the chemical kinetic analysis. The results show that the addition of n-butanol greatly robs the free radicals generated by the lowtemperature reaction of biodiesel thereby weakens the low-temperature reaction path of biodiesel.