The aim of this study was to develop an Administrative Ethical Behaviour Scale (AEBS) and to determine whether nurses found their head nurses' behaviours ethical and to reveal head nurses' ethical and unethical administrative behaviour. It was conducted on 264 nurses working in five state hospitals in Trabzon, Turkey. Content validity index of the scale was 0.87, item-to-total correlations ranged from 0.50 to 0.81 and Chronbach Alpha was 0.98. The scale included five subscales, i.e. truthfulness and honesty, liabilities and supremacy of laws, rights and freedom, good human relationships and humanism, justice and equality. Overall, head nurses' behaviour was considered ethical by nurses; however, their behaviour in terms of justice and equality, good human relationships and humanism was not found ethical. Positions, satisfaction with head nurses' behaviour and frequency of contact with them affect nurses' opinions.