This study examined the relationship between nurses' ethical decision-making levels and their professional behaviours. Data were collected from 225 nurses who were recruited from university hospitals in Ankara using proportionate sampling. Data were analysed using descriptive statistics and Pearson correlations. Most of the nurses were familiar with ethical dilemmas in nursing practice. The Nursing Principled Thinking level was above average, while the Practical Consideration level was average. Nurses' professionalism level was low. There was a positive but weak correlation between professional behaviours of the nurses and their ethical decision-making levels. Increasing nurses' professionalism level can provide a positive contribution to the ethical decision-making level.