Materiality in private sector financial audit is a topic that has been relatively well developed in the literature. Specific research in this regard in public sector auditing, on the other hand, is scarce at the international level and absent in Brazil. In view of this, the purpose of this study was to identify the parameters used to determine materiality in public sector financial audit. To this end, we sent questionnaires to the 192 Supreme Audit Institutions that are members of INTOSAI and to 36 Brazilian public auditors, specialists in financial audit, who are staff members of the TCU or the CGU seeking information with respect to the Institutions’ guidelines and the auditors’ perceptions about materiality. Results reveal that expenditures, revenues and total assets are the benchmarks most recommended by respondents for defining materiality in the public sector. In addition, they recommended the adoption of percentages of up to 2% for each of these parameters in defining what is material. It was observed, as well, especially with respect to the effectiveness of internal control and to public expectations or interests, that qualitative aspects should be also taken into account in determining materiality, although a lesser degree of importance is attributed to this than to the quantitative aspects,. The study contributes to the accounting literature on the development of audits, particularly with respect to the use of a concept, materiality, that is always emphasized in professional standards, but about which there are few objective guidelines.