The constitutive model and microstructure evolution of Ti65 alloy were investigated through isothermal compression experiments. The results showed that the alloy exhibits a bimodal microstructure, which is characterized by a combination of coarse and fine grains. The hot deformation behavior of the alloy was found to be influenced by the microstructure, with the coarse grains exhibiting a higher strain rate sensitivity than the fine grains. The study provides valuable insights into the deformation behavior and microstructure evolution of Ti65 alloy, which is essential for its application in high-temperature applications.