When female kangaroos are shot during commercial harvesting, it is a requirement that dependent young-at-foot are euthanased. However, there are anecdotal reports that harvesters either cannot euthanase young-at-foot (eg they do not see them or they flee) or will not (eg they do not think it is necessary). In this study we used the theory of planned behaviour to understand the beliefs, attitudes and behaviour of kangaroo harvesters with regards to the euthanasia of young-at-foot. We firstly conducted a survey of a small number of kangaroo harvesters (n = 21) to gather information to develop the main questionnaire. Recruitment of participants was conducted using a number of approaches including a mail out of over 600 pen-and-paper questionnaires to harvesters in NSW, QLD and SA, Australia. We received completed questionnaires from 65 harvesters. Behaviour was directly observed in only 14 harvesters. The results indicated that those kangaroo harvesters with a more favourable attitude towards euthanasing young-at-foot and who feel more social pressure to do so are more likely to intend to euthanase young-at-foot. However, intention to euthanase orphaned young-at-foot only rarely translated into actual behaviour. The participating harvesters believe that euthanasing young-at-foot reduces joey suffering; that government kangaroo management agencies and farmers and graziers approve of them doing it (but animal protection groups do not); and that the greatest limiting factor preventing them from euthanasing young at-foot is that they escape. This research revealed deficiencies in knowledge and training of kangaroo harvesters with regard to humane harvesting practices. We conclude that the use of social psychology methodology and frameworks, such as the theory of planned behaviour, can provide a detailed insight into human attitudes and behaviours that affect animal welfare. This approach can reveal the most important specific factors to consider when training and educating personnel who have direct responsibility for the humane treatment of animals.