The aim of this work is to determine the importance and level of effectiveness of audit committees as one of the main elements of corporate governance through a theoretical framework and empirical research. Data for analysis were taken from the Yearly corporate governance questionnaire, by the aim of the research, a sample is collected, based on 2018 information for companies listed on stock exchange list. The focus of the analysis is on the characteristics and presence of audit committees within Croatian listed companies and their relationship with internal and external audit in the corporate governance process. The Efficiency index of audit committee (EIAC) is based on 10 questions from the Yearly questionnaire of corporate governance codex for each company individually for 2018. The results of the analysis show that 86.30% of the observed companies have an established Corporate Governance Codex, and 72.60% of the observed companies have an established audit committee. The research showed that the most common value of the efficiency index is 70%, which would mean the average efficiency of audit committees in the Republic of Croatia. It was found that there is no interdependence between the performance of companies measured by ROA and ROE indicators and the efficiency of audit firms. Ultimately, it was concluded that companies whose members of the audit committee are also members of the supervisory board have a higher efficiency index. With the aim of better future implementation and practice of corporate governance in Croatia, the base of issues of the Corporate Governance Codex related to the work of audit committees should be expanded to analyze the performance of companies.