Cyber bystanders may reduce the frequency and impact of cyberbullying incidents they witness. Recent evidence indicates that bystanders can employ constructive (e.g. comforting the victim) or aggressive (e.g. threatening the bully) strategies when intervening in cyberbullying incidents. The aim of this study was to develop a questionnaire to measure aggressive and constructive forms of bystander intervention (the Styles of Bystander Intervention Scale), as well as to investigate the influence of moral disengagement on these behaviours. Participants were 301 ethnically diverse Australian adolescents aged 12-17 years (M[subscript age] = 14 years 6 months), who completed a self-report survey to examine bystander intervention styles and the associations with moral variables. The Styles of Bystander Intervention Scale demonstrated adequate reliability and effectively distinguished between aggressive and constructive forms of intervention. The results indicated that higher moral disengagement was significantly associated with aggressive bystander responses, and lower moral disengagement was significantly associated with constructive responses. These results highlight the need to differentiate between aggressive and constructive bystander intervention and the importance of investigating psychological factors related to these intervention styles.