This study aims to investigate the influence of internal auditors’ competence on the effectiveness of an internal audit, with Islamic spiritual quotient as a moderating variable. The Islamic Spiritual Quotient (ISQ) instrument is derived from the four prophetic pillars, namely siddiq (truthfulness & integrity ), amanah (trustworthiness), fathanah (competent & skillfull) and tabligh (advocacy & communication). Using questionnaires distributed to 38 internal auditors of Islamic financial institutions (IFIs) in Indonesia, the data were analysed using the structural equation model (SEM) based on partial least squares (PLS). As hypothesised, the findings show that the personal competence of internal auditors improves the effectiveness of an internal audit. Interestingly, ISQ clearly strengthens the positive influence of personal competence on internal audit effectiveness. The stronger the ISQ of internal auditors, the stronger the influence of individual competence on internal audit performance.