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Data on the re-administration of epidermal growth factor receptor (EGFR)-tyrosine kinase inhibitors (TKIs) after osimertinib failure in patients with T790M-positive non-small cell lung cancer (NSCLC) is limited. EGFR-TKI re-administration efficacy may vary between patients with T790M loss and those with T790M persistent with re-biopsy after osimertinib treatment. Patients who received EGFR-TKI re-administration (gefitinib, erlotinib, afatinib, dacomitinib, and osimertinib) after osimertinib failure were identified from our database. T790M mutation status before EGFR-TKI re-administration was analyzed via repeat biopsy. We retrospectively evaluated the efficacy of EGFR-TKI re-administration, especially differences according to the T790M mutation status, via repeat biopsy. Until June 2020, 28 patients received EGFR-TKI re-administration and 17 underwent repeat biopsy after osimertinib failure. Patients were divided into three groups, including the T790M loss group, where active mutation persisted and T790M was lost (13/17); T790M remaining group, where both the active mutation and T790M persisted (3/17); and active mutation loss group where both the active mutation and T790M were lost (1/17). The overall response rate (ORR) of EGFR-TKI re-administration in the T790M loss group was 31% and the disease control rate (DCR) was 54%, which were higher than the ORR of 21% and DCR of 43% in the entire patient population. ORR and DCR of the not re-biopsy group were low (9% and 27%, respectively). The therapeutic effect of EGFR-TKI re-administration in patients with T790M-positive NSCLC after osimertinib failure is limited. EGFR-TKI re-administration may be considered in cases of T790M loss after repeat biopsy.