INTRODUCTION:Flumatinib mesylate is a derivative of imatinib and has higher selectivity and potency toward BCR::ABL1 kinase compared with imatinib. Flumatinib was approved patients with newly diagnosed CML-CP in China. We analysed the efciency and safety of flumatinib in CML patients resistant or intolerant to Imatinib in the real word. METHODS:164 adult CML-CP patientsrecieved flumatinib as 2nd line therapy after imatinib were collected from 18 centers in china. The primary outcome was to demonstrate the probabilities of responses including complete hematologic response (CHR), cytogenetic response, and molecular response (MR) after the later line of flumatinib. The secondary outcome was to assess adverse events (AEs). The diagnosis and response evaluation were dened according to the European Leukemian Net 2020 recommendations. The side effect were graded according to the National Cancer Institute Common Terminology Criteria for Adverse Events Version 4.0. Results: 164 patients with CML-CP with a median age of 51 (range: 17-87) years were included, 95(57.9%) males. The medium interval from imatinib to flumatinib was 13.2(1-185) months. The median dosage of flumatinib was 600 mg/day. 127 patients had ELTS information with 84 (66.1%), 30 (23.6%), 13 (10.2%) patients in low-, medium-, and high risk groups, respectively. ABL mutations were detected in 144 patients before initiating flumatinib, 5 (3.5%) patients had ABL mutations with 1 patient each showing E279K, E459K, M351T mutation; and 2 patients had F317L mutation. I 56 (34.1%) patients had optimal response but intolerant to imatinib, whereas 43 (26.2%), 65 (39.5%) patients had suboptimal or failure response to imatinib. The median duration of flumatinib treatment was 10.9 (2-25.46) months. Discontinuation of flumatinib treatment was observed in 17 (11%) patients, with a median treatment duration of 8.8 (2-25.46) months. The probabilities of CHR, CCyR/MR 2 , MMR, and MR4 or better at baseline and after flumatinib therapy have been represented in Table 1. The patients without evaluable data were considered without response. The rate of CHR, CCyR/MR 2 , MMR and MR4 or better were 86% (141/164), 48.2% (79/164), 15.2% (25/164) and 7.9% (13/164) at baseline increased to 97.6% (160/164). 81.1% (133/164), 65.2% (107/164), 34.8% (57/164) respectively during flumatinib treatment. The probabilities of response from CHR to MR after flumatinib therapy were analyzed based on clinical parameters.