A process for working .beta. titanium alloy comprises the steps of first elongating the alloy at a temperature not higher than a .beta. transus temperature and at a working ration of 30% or more. Next, conducting a subsequent aging treatment. Then, elongating the alloy at a temperature not higher than the aging treatment temperature and at a working ratio of 70% or more when combined with that in the first step for elongating. Then a recrystallization treatment is carried out at a treating temperature not higher than the .beta. transus temperature or isothermal working is carried out within a temperature range of the .beta. transus temperature minus 200.degree. C. to the .beta. transus.