Abstract: The as-cast structure and microstructure obtained after heat-treatment in the α+γ field of a Ti-46Al-8Nb-2Mn-0.2B alloy were studied. Optical and SEM observations show that the γ phase segregation region is not the grain boundary of the alloy but part of the α + γ lamella. The Al content at the γ phase segregation region is a little more than the α + γ lamella matrix, but it can play an important role in stabilizing the lamella and does harm to the break-up at the γ phase segregation region. By obtaining near γ microstructure firstly in the alloy and then heat-treating it in the middle region of the α + γ field, the duplex microstructure with a grain size of 40μm can be formed, but a little of β phase still exists.