Superplastic forming provides a good way for Ti alloys which are usually difficult to be deformed. Ti75 alloy with a nominal composition of Ti-3Al-2Mo-2Zr is a newly developed corrosion resistant alloy, with a middle strength and high toughness. In the present paper, superplastic behavior of the alloy was investigated, the microstructural evolution in superplastic deformation was observed and the superplastic deformation mechanisms were analyzed. The results showed that the strain rate sensitivity, in, of the Ti75 alloy was larger than 0.3 and the strain was over 2.0 without surface cracking at 800 degrees C and 5x10(-4)s(-1) in compressive testing. During the first stage of superplastic deformation, alpha phase grains became equiaxed, fine and homogeneous due to the recrystallization in alpha phase and diffusion in beta phase. Newly formed equiaxed alpha grains then could slide and rotate, exhibiting superplastic features. The stress concentration caused by grain sliding of alpha grains could be released by slip and diffusion in beta phase between the alpha phase grains, which acted as accommodation mechanisms.