We examine the effectiveness of mandatory audit-partner rotation in promoting audit quality using audit data in Taiwan where a five-year audit-partner rotation became de facto mandatory in 2004. Using both absolute and signed abnormal accruals and abnormal working capital accruals as proxies for audit quality, we find some evidence that audit quality of companies subject to mandatory audit-partner rotation in 2004 is higher than audit quality of companies not subject to rotation in 2004. However, audit quality of companies subject to mandatory rotation in 2004 is lower than audit quality of these same companies in 2003 under the old audit partners. Furthermore, audit quality of companies subject to mandatory rotation in 2004 is indistinguishable from audit quality of companies whose audit partners were voluntarily rotated before 2003. Therefore, the effect of mandatory audit-partner rotation on audit quality, in terms of auditors constraining management's extreme income-increasing or extreme income-decreasing accruals, is mixed. In contrast, using earnings response coefficients as a proxy for investor perceptions of audit quality, we consistently find that investors perceive mandatory audit-partner rotation as enhancing audit quality, suggesting that mandatory audit-partner rotation enhances auditor independence in appearance.