Objective To investigate the clinical and biological features of patients with mixed﹣phenotype acute leukemia (MPAL). Methods The clinical data of 24 de novo adult patients with MPAL who were admitted to Fujian Medical University Union Hospital from January 2012 to October 2018 were retrospectively analyzed. These patients were diagnosed according to the World Health Organization (WHO) 2016 criteria. The clinical and biological characteristics of the patients were analyzed by morphological and cytochemical staining, immunophenotyping, cytogenetics and molecular biology. Results Of the 24 patients, 16 were male and 8 were female, and the median age of the patients at diagnosis was 27 years old (5-66 years old). The average blasts of bone marrow were (57.41 ±23.20)% . Thirteen cases (54.2% ) were diagnosed as MPAL morphologically, while 5 cases (20.8% ) were diagnosed as acute myeloid leukemia (AML), 5 cases (20.8%) were diagnosed as acute lymphoblastic leukemia (ALL) and 1 case (4.2%) was inconclusive. Eighteen patients (75.0%) co﹣expressed B﹣lymphoid and myeloid markers, while 5 patients (20.8%) with T﹣lymphoid and myeloid markers and 1 patient (4.2%) with B﹣lymphoid and T﹣lymphoid markers, respectively. The positive rate [median (range)] of CD38, HLA﹣DR and CD34 was 90.5% (0.1%-99.7%), 90.1% (1.1%-98.8% ) and 81.3% (0.1%-97.8%), respectively. Eighteen cases underwent chromosome examination, of which 5 cases carried with t(9;22)(q34;q11), 3 cases with t(v;11q23.3), 2 cases with complex karyotypes, and 2 cases with t(9;22)(q34;q11) and complex karyotypes, respectively. Twenty﹣one cases underwent genetic examination, of which 6 cases were positive for BCR﹣ABL, 3 cases were positive for MLL, 1 case was positive for MLL and BCR﹣ABL, 1 case was positive for BCR﹣ABL and TP53, and 1 case was positive for PHF6 and ASXL1 respectively. Of the 24 patients, 7 refused chemotherapy and 17 received induction chemotherapy. Of the patients receiving chemotherapy, 9 cases achieved complete remission (CR), 1 case was partial remission (PR), and 7 cases were not relieved (NR). In 11 patients treated by ALL﹣type induction regimen and 6 patients treated by ALL and AML﹣type induction regimen, 8 cases and 1 case achieved CR, the difference in CR rate was statistically significant (P<0.05). In 6 patients with Philadelphia chromosome (Ph) positive and 11 patients with Ph negative, 1 case and 8 cases achieved CR, the difference in CR rate was statistically significant (P<0.05). The median follow﹣up time was 5.5 months (0-36 months). The 3﹣year overall survival (OS) rate was 17.5% and the median OS time was 6 months. The 3﹣year OS rates in the allogeneic hematopoietic stem cell transplantation and non﹣transplanted groups were 75.2% and 0, respectively, and the median OS time was not reached and 4 months (P< 0.05). Conclusions MPAL is rare, it mostly co﹣expresses lymphoid and myeloid antigens and shows a much higher incidence of CD34, CD38 and HLA﹣DR. MPAL is often associated with Ph positive and complex karyotypes. MPAL has a low remission rate and poor prognosis, and a reasonable and effective treatment plan should be further explored.