This is a dataset on defensive behaviour in response to simulated intergroup conflict in banded mongooses, collected from a wild population of banded mongooses on the Mweya Peninsula, Queen Elizabeth National Park, Uganda between 2016-2017. We experimentally simulated conflict between rival social groups of banded mongooses and recorded data on behavioural responses including interaction with the stimulus, defensive behaviours such as standing upright, scent marking, and attacking, and the cohesion of behavioural responses within the group. These data were collected to examine collective defence behaviour in the face of intergroup conflict.