Objective To establish a cytotoxic T-lymphocyte-associated protein 4 ( CTLA4) humanized mice model, and to provide an effective mouse model for CTLA4-targeted cancer therapeutic antibody research, development, and screening. Methods The animal models were established by CRISPR/ Cas9 and then analyzed by polymerase chain reaction ( PCR), reverse transcription-PCR ( RT-PCR), western blotting, hematoxylin-eosin ( HE ) staining and fluorescence-activated cell sorting. The mouse melanoma cell line ( B16 ) was injected subcutaneously into CTLA4 humanized mice to observe the anti-tumor effects of intraperitoneal injection of the CTLA4 monoclonal antibody, ipilimumab. Results CTLA4-humanized mice could stably express human CTLA4 but not murine CTLA4. CTLA4- humanized mice survived normally within 6 months after birth, and there were no obvious abnormalities in histopathology and the immune system. In CTLA4-humanized mice, ipilimumab slowed tumor growth. CTLA4-knockout mice did not express CTLA4 and died of autoimmune diseases within 3 ~ 5 weeks after birth. Conclusions CTLA4-humanized and CTLA4-knockout mice were established. CTLA4-humanized mice can be used as an animal model for therapeutic antibody- and CTLA4 gene-related drug experiments.