Objective To investigate the genetic alterations and histopathological features of IDHmutant astrocytoma grade 4. Methods From July 2021 to July 2022， in the Department of Neurosurgery of Beijing Tiantan Hospital affiliated to Capital Medical University， a total of 73 patients were recruited， who undertook surgery treatment and diagnosed as IDH-mutant astrocytoma grade 4 by postoperative histopathology. These cases' epidemiological and morphological characteristics were gathered and studied. The second generation sequencing method was used to detect the molecular pathology characteristics of tumors； Immunohistochemical staining was used to detect the characteristic protein expression in tumor cells. Results The median age of the IDH-mutant astrocytoma grade 4 patients （n=73） was 38 years old， male accounting for 56.2% （41/73）. 75.3% （55/73） of the tumors were in the frontal lobes. Necrosis and/or microvascular proliferation were absent in 13.7% of the tumors， which histopathological grade conforms to grade 2/3 astrocytoma. Other 86.3% （63/73） of tumors showed microvascular proliferation and necrosis， consistent with the characteristics of grade 4 astrocytoma. Immunohistochemistrical examination revealed significant IDH R132H positivity in the 73 tumors. The positive rate of P53 was 88.1% （59/67）. The loss of ATRX （α-thalassemia/mental retardation， X-linked） expression is 83.6% （56/67）. Molecular pathology test results showed that all patients had IDH1 R132H mutation. The promoter region of O-6-methylguanine DNA methyltransferase was methylated in 76.7% （56/73） of patients， and the mutation rate of TP53 and ATRX was 96.6% （57/59） and 64.3% （36/56） respectively. The proportion of homozygous deletion of cyclin dependent kinase inhibitor 2A/B （CDKN2A/B） was 46.6% （34/73）. Conclusions Necrosis and/or microvascular proliferation can be seen in the majority of grade 4 IDHmutant astrocytomas. However， some cases with homozygous CDKN2A/2B deletion displayed morphological characteristics aligned to lower-grade astrocytomas. For IDH mutant astrocytomas， molecular pathological testing including CDKN2A/B copy number is necessary.