The biochemical mechanism of resistance of 9 Aegilops species including A.biuncialis,A.juvenalis, A.ovata, A.kotschyi var. varianilis, A.triaristata, A.tauschii, A.vavilovii, A.crassa and A.ventricosa in Triticeae to oat bird cherry aphid ( Rhopalosiphum padi ) were reported for the first time. The results showed that the content of total phenols in seedling was not associated with resistance to this aphid. The level of DIMBOA was negatively related to intrinsic innate rate of increase ( r m ) of R. padi. Neither of soluable sugar nor total phenols in adult stage was associated with resistance level. However, concentrations of free proline and serine in leaf were positively related to r m of R. padi ( r m =0.0636+0.23x pro ** +1.982x ser *). The content of DIMBOA was high negatively related to r m of R. padi ( r =0.819 ** ). The low level of free proline and serine and high concentration of DIMBOA could be regarded as important elements for resistance of Aegilops species to R. padi. The biochemical mechanism of resistance of 9 Aegilops species including A. biuncialis, A.juvenalis, A.ovata, A.kotschyi var. Varianilis, A.triaristata, A.tauschii, A.vavilovii, A..crassa and A.ventricosa in Triticeae to oat bird cherry aphid (Rhopalosiphum padi) were reported for the first time. The results showed that the content of total phenols in seedling was not associated with resistance to this aphid. The level of DIMBOA was negatively related to intrinsic innate rate of increase ( rm) of R. padi. ​​Neither of soluable sugar nor total phenols in adult stage was associated with resistance level. However, concentrations of free proline and serine in leaf were positively related to rm of R. padi (rm = 0.0636 + 0.23x pro ** + 1.982x ser *). The content of DIMBOA was high negatively related to rm of R. padi (r = 0.819 **). The low level of free proline and serine and high concentration of DIMBOA could be regarde d as important elements for resistance of Aegilops species to R. padi.