The thesis deals with the effect of professional ethics on the work quality of external auditors. The term external auditors refers to auditors who audit financial statements. While performing an audit of financial statements, auditors must comply with certain rules and principles contained in the Code of ethics for professional accountants (auditors). The paper tries to explain why external auditors must act in accordance with the Code of professional ethics and what impact it has on the quality of external auditor's work. The thesis is divided into three main chapters. The first chapter theoretically explains the concept of audit and its types, the auditor's role in the audit of financial statements, the fundamental determinants of audit quality and its control system in the Republic of Croatia. The second chapter defines ethics and ethical principles, the concept of an ethical dilemma and explains the importance of the auditor's professional ethics for the quality of the financial statements audit. The third part analyzes the research conducted through a survey on the effect of professional ethics on the work quality of external auditors. The conclusion is that professional ethics has an effect on the work quality of external auditors and while observing the Code of professional ethics, external auditors protect the interests of the financial statements users and increases confidence in the work quality of auditors and the auditing profession as a whole.