Background: ASK120067 (Limertinib) is a newly developed third-generation epidermal growth factor receptor (EGFR) tyrosine kinase inhibitor (TKI) targeting both sensitizing EGFR and EGFR T790M mutations. This study aimed to evaluate the efficacy and safety of ASK120067 in patients with locally advanced or metastatic EGFR T790M mutated non-small cell lung cancer (NSCLC). Methods: This study was a single-arm, open-label, phase 2b study conducted at 62 hospitals across China. Patients with locally advanced or metastatic NSCLC with centrally confirmed EGFR T790M mutations in tumor tissue or blood plasma who progressed after first or second generation EGFR TKIs or with primary EGFR T790M mutations were enrolled. Patients received ASK120067 160mg orally twice daily, until disease progression, or unacceptable toxicity. The primary endpoint was objective response rate (ORR) assessed by Independent Review Committee (IRC) per RECIST1.1. Secondary endpoints included disease control rate (DCR), progression-free survival (PFS), duration of response (DOR), overall survival (OS), and safety. Safety was assessed according to CTCAE 4.03. Results: Between June 24th, 2019 and Feb 25th, 2021 301 patients were enrolled and received ASK120067 treatment. All patients entered the full analysis set (FAS) and safety set (SS). A total of 99 (32.9%) patients had central nervous system (CNS) metastases at baseline. By the data cutoff date on Sep 9th, 2021, 76 (25.2%) remained on treatment. The median follow-up time was10.4 (range 0.3-26.3) months. Based on FAS, the IRC-assessed ORR was 68.8% (95%CI 63.2%-74.0%) and DCR was 92.4% (95%CI 88.8%-95.1%). The median PFS was 11.0 (95%CI 9.7-12.4) months, median DOR was 11.1 (95%CI 9.6-13.8) months, and median OS was not reached (NR) (95%CI 19.7 months-NR). Objective responses were achieved across all pre-specified subgroups. For 99 patients with CNS metastases, the ORR was 64.6% (95%CI 54.4%-74.0%), median PFS was 9.7 (95%CI 5.9-11.6) months, and median DOR was 9.6 (95%CI 8.1-15.2) months. For 41 patients who had evaluable CNS lesion, the confirmed CNS-ORR was 56.1% (95%CI, 39.7%-71.5%) and median CNS-PFS was 10.6 (95%CI 5.6-NE) months. In SS, 289 (96.0%) patients experienced at least one adverse drug reaction (ADR), with the most common being diarrhea (81.7%), anemia (32.6%), rash (29.9%) and appetite decrease (28.2%). Grade ≥3 ADRs occurred in 104 (34.6%) patients, and the most common included diarrhea (13.0%), hypokalemia (4.3%), anemia (4.0%) and rash (3.3%). ADRs leading to dose interruption and dose discontinuation occurred 24.6% and 2% of patients, respectively. No ADR leading to death occurred. Conclusions: ASK120067 demonstrated promising efficacy and an acceptable safety profile for the treatment of patients with locally advanced or metastatic EGFR T790M mutated NSCLC. Clinical trial information: NCT03502850.