This study investigates the relations between auditor tenure and audit quality. Our study is motivated by the regulator's rule to call for ”mandatory auditor rotation”. We use abnormal accruals as proxies for audit quality to examine whether extended tenure impairs auditor's independence and results in audit quality reduced. The empirical results indicate that, under the current voluntary rotation regime in Taiwan, audit quality does not deteriorate over time as the auditor-client relationship lengthens. In opposition to the opinion of regulator in audit tenure, we do find that absolute abnormal accruals decline with auditor tenure. In. other words, longer audit tenure constrains managerial discretions with accounting accruals, whether income-increasing or income-decreasing manipulations. These results are robust to several sensitivity analyses.