Background: The literature indicates that separate significant links exist in adolescence between empathy, cognitive and affective motivation to defend victims, and behavioural problems in bullying episode in schools. Aims: The aim of the study was to investigate the relationship between empathy, motivation to defend, and defending behaviour in bullying situations. The hypothesis focuses on the possible role of autonomous motivation in the association between empathy and defending attitudes. Samples and methods: Data were collected from 430 Italian adolescents (48.4% male, 51.6% female) who completed a questionnaire in their schools. The mean age of the participants was 13.1 years (SD = 2.1). Results: Results showed that empathy significantly predicts defending behaviour and also has a significant effect on extrinsic, introjected, and intrinsic motivation to defend. Autonomous motivation, in turn, has a mediating role in the relationship between empathy and defending behaviour. Conclusions: Our study suggests the importance of focusing on empathy and on developing autonomous motivation to defend in children, to raise spontaneous defending attitudes against bullying. © 2019 The British Psychological Society