Influenza pandemics occur several times per century, causing millions of deaths. Influenza A viruses (IAVs) are highly infectious viral pathogens capable of crossing interspecies barriers and infect a wide range of avian and mammalian species. In 2017, an H9N2 virus was isolated for the first time from Egyptian fruit bats (Rousettus aegyptiacus). Phylogenetic analyses revealed that bat H9N2 is descended from a common ancestor dating back centuries. However, the bat H9 sequences appear to be genetically similar to current avian IAVs, suggesting recent reassortment events. These observations raise the question of the zoonotic potential of the mammal-adapted bat H9N2. Here, we report the cryo-EM structure of bat trimeric HA protein and its complex with receptor-binding site-specific antibody at high resolution. We also characterised the affinities for the multiple cross-reactive monoclonal antibodies. These results provide structural evidence of a close evolutionary relationship and may offer insights into the evolution and cross-species transmission of influenza.