Objective To explore the hematology adverse reactions of imatinib mesylate (IM) in the treatment of chronic phase (CP) of chronic myeloid leukemia (CML).Methods The clinical data of 435 CML-CP patients treated with IM were analyzed respectively in the Affiliated Cancer Hospital of Zhengzhou University from Jan 2013 to Jan 2015.The hematology adverse reactions were followed up regularly and the incidences in different groups with various factors were compared.Results Until the end of follow-up,74 (17.0 ％) patients had hematology adverse reactions.61 (14.02 ％) patients had neutropenia,including 9 (14.75 ％) patients who had level Ⅲ-Ⅳ neutropenia.60 (13.79 ％) cases had thrombocytopenia including 11 (18.33 ％) patients with level Ⅲ-Ⅳ thrombocytopenia.Anemia occurred in 50 (11.49 ％) patients,of whom 5 (10.00 ％) cases were grade Ⅲ-Ⅳ anemia.33 (7.59 ％) cases experienced pancytopenia.The incidence of hematology adverse reactions was influenced by nine factors,including the course before treatment,the size of spleen,Sokal scores,the use of interferon,fusion genes,chromosomes,complete cytogenetic response,main molecular reaction and Karnofsky scores (all P ＜ 0.05),while it was not influenced by age,gender,BMI,smoking and drinking (all P ＞ 0.05).Conclusions During the initial treatment of CML-CP,if patients experienced level Ⅰ-Ⅱ hematology adverse reactions,they can continue to taking IM.However,when level Ⅲ-Ⅳ hematology adverse reactions happened,they need to reduce the dose or stop taking,and one month later,hemocyte will get well.In the long-term treatment of CML,once level Ⅲ-Ⅳ hematology adverse reactions occur,the patients need to receive some related inspections,such as bone marrow morphology and molecular biology detection,to clear the disease stage.When it is necessary,the patients can take the second generation of tyrosine kinase inhibitors.