The secondary T790M mutation in epidermal growth factor receptor (EGFR) is the major mechanism of acquired resistance to EGFR tyrosine kinase inhibitors (TKI) in non-small cell lung cancer (NSCLC). Although irreversible EGFR TKIs, such as afatinib or dacomitinib, have been introduced to overcome the acquired resistance, they showed a limited efficacy in NSCLC with T790M. Herein, we identified the novel de novo resistance mechanism to irreversible EGFR TKIs in H1975 and PC9-GR cells, which are NSCLC cells with EGFR T790M. Afatinib activated interleukin-6 receptor (IL-6R)/JAK1/STAT3 signaling via autocrine IL-6 secretion in both cells. Inhibition of IL-6R/JAK1/STAT3 signaling pathway increased the sensitivity to afatinib. Cancer cells showed stronger STAT3 activation and enhanced resistance to afatinib in the presence of MRC5 lung fibroblasts. Blockade of IL-6R/JAK1 significantly increased the sensitivity to afatinib through inhibition of afatinib-induced STAT3 activation augmented by the interaction with fibroblasts, suggesting a critical role of paracrine IL-6R/JAK1/STAT3 loop between fibroblasts and cancer cells in the development of drug resistance.