Journal of Business Theory and Practice ISSN 2372-9759 (Print) ISSN 2329-2644 (Online) Vol. 6, No. 2, 2018 www.scholink.org/ojs/index.php/jbtp 118 Original Paper Corporate Governance on the Performance of Internal Auditors in Thailand Public Limited Company Sutana Narkchai 1* , Faudziah Hanim Binti Fadzil 1 & Sompon Thungwha 2 1 Othman Yeop Abdullah Graduate School of Business, University Utara Malaysia, Sintok, Malaysia 2 Faculty of Business Administration, Ramkhamhaeng University, Bangkok, Thailand * Sutana Narkchai, Othman Yeop Abdullah Graduate School of Business, University Utara Malaysia, Sintok, Malaysia Received: March 12, 2018 Accepted: March 19, 2018 Online Published: April 2, 2018 doi:10.22158/jbtp.v6n2p118 URL: http://dx.doi.org/10.22158/jbtp.v6n2p118 Abstract The issue of performance of internal auditors is important since Thailand was also affected by the accounting scandals. The expanded scope in the definition of internal auditing and new regulatory requirements such as the Sarbanes-Oxley Act 2002 has increased the demands on internal auditing. This study was conducted to examine the relationship between the corporate governance on the performance of internal auditors in Thailand public limited companies. In this study, corporate governance relates to the board of directors size and audit committee size to the performance of the internal auditor. To achieve this objective, two hypotheses were developed based on previous studies and the agency theory. Survey questionnaires were sent to the Chief Audit Executives (CAEs) to determine the effectiveness on their performance based on the professional standards issued by the IPPF (2017) indicators. A total of 520 questionnaires were distributed, but only 146 were usable. Multiple regressions were used to test the relationship between the variables. The result showed that there is insignificant relationship between board of director’s size and internal auditors’ performance. This study however found that audit committee size has a positive relationship on the performance of internal auditors. Therefore, audit committee need to increase higher responsibility with regard to corporate governance by overseeing financial reporting and internal control matters. Keywords performance of internal auditors, corporate governance, IPPF, Thailand Public Limited Company 1. Introduction Performance of internal auditors can be encountered with significant diversity and vagueness in their work. They need skills in examining activities and management practices. They can be faced with the need to become familiar with organizational contexts and subject matters. Performance auditors must have a clear understanding of the objectives, the effectiveness of operation, and compliance with laws, regulations and policies, audit standards and process. Performance measurement includes establishment of standards and indicators to which management and staff are held accountable. Recently, performance measurement obtained rational attention in internal auditing because it establishes one of the most essential managerial functions (Rupsys & Boguslauskas, 2007). With this basis, performance measurement evaluates to what extent the efficiency of public resources