I examine whether and how the introduction of an internationally credible audit regulatory oversight affects a firm’s debt concentration level in a cross-country setting. For a sample of non-US-listed companies across 45 countries, I observe a significant decrease in a firm’s debt concentration after its auditors’ initial inspection report released by the US Public Company Accounting Oversight Board (PCAOB), but I do not observe a difference when the auditor is subject to the inspection by the local audit regulator. The effects are more pronounced in cases when foreign debt investors are likely to involve, consistent with the notion that foreign debt investors consider the PCAOB inspection program a more credible assurance mechanism that mitigates the co-ordination costs among debtholder groups than inspection programs enforced by local audit regulators. Cross-sectional results across a range of auditor-level, client-level and country-level characteristics are also consistent with this explanation. Overall, the findings highlight the role of credible audit oversight in shaping a firm’s efficient debt structure concentration especially when foreign debts are involved.