In this thesis, with the help of the conducted research, was analysed and presented the importance of ethics and the perception of ethical and unethical behaviour in the auditor's business. Furthermore, auditing as a profession is presented, auditing principles, standards and values of the audit profession are analysed as well. The concept of professional ethics and the Code of Ethics, the institutional framework of ethics, the rules of professional conduct of auditors, the IFAC Code of Professional Ethics and how independence of auditors, corporate social responsibility and professional scepticism affect ethics, are also explained. The thesis also presents the most common forms of auditor's unethical behaviour, ways of ensuring the auditor's ethical behaviour through training and education, the difference between fraud and error, conflict of interest and ethical dilemmas. In order to achieve the set goals of this research, a survey was conducted. The target group of this research are audit firms and auditors operating in the territory of the Republic of Croatia, who will be asked questions regarding ethical and unethical behaviour. The questionnaire respondents presented answers to questions with the aim of obtaining final results and creating a clearerpicture of the importance of ethics and the perception of ethical and unethical behaviour in the auditor's business.