A process for producing a heat-resistant Ti alloy having a composite structure having an equiaxed α phase and β grains containing an acicular α phase inside thereof, the process comprising: a step of preparing a bulk alloy having a composition consisting of, in terms of % by mass: 5.0-7.0% of Al; 3.0-5.0% of Sn; 2.5-6.0% of Zr; 2.0-4.0% of Mo; 0.05-0.80% of Si; 0.001-0.200% of C; 0.05-0.20% of O; and 0.3-2.0% in total of at least one kind selected from the group consisting of Nb and Ta; and optionally, 0.005-0.200% of B; 0.2% or less of N; 0.2% or less of Fe; 0.2% or less of Ni; and 0.2% or less of Cr; with the balance being Ti and unavoidable impurities, a first heat treatment step in which the alloy is heated and held at a temperature that is within a β-single-phase temperature region and is higher than a β transformation point T β, an adjustment forging step in which the alloy is hot-forged at a temperature that is within an (α+β)-two-phase temperature region and is lower than the β transformation point T β, thereby adjusting an equiaxed α phase, a second heat treatment step in which the alloy is heated and held at a temperature that is within the (α+β)-two-phase temperature region and is higher than the temperature in the adjustment forging step, followed by cooling to precipitate an acicular α phase, and an aging heat treatment step which is performed at 570-650°C, wherein, prior to the first heat treatment step, the alloy is subjected to a pre-forging step in which the alloy is hot-forged in the β-single-phase temperature region and further hot-forged in the (α+β)-two-phase temperature region, whereby the acicular α phase is formed in the β-grains, and the equiaxed α phase has an average grain diameter of 5 μm to 20 μm and an average aspect ratio of 5.0 or less and is contained in an amount of 5-35% in terms of sectional areal proportion to the composite structure, wherein the pre-forging step is a step in which the alloy is hot-forged in the β-single-phase temperature region and further hot-forged in an (α+β)-two-phase temperature region of [(T β -100°C) or higher and lower than T β] so as to result in a total forming ratio in the forging of 3 or higher. a step of preparing a bulk alloy having a composition consisting of, in terms of % by mass: 5.0-7.0% of Al; 3.0-5.0% of Sn; 2.5-6.0% of Zr; 2.0-4.0% of Mo; 0.05-0.80% of Si; 0.001-0.200% of C; 0.05-0.20% of O; and 0.3-2.0% in total of at least one kind selected from the group consisting of Nb and Ta; 5.0-7.0% of Al; 3.0-5.0% of Sn; 2.5-6.0% of Zr; 2.0-4.0% of Mo; 0.05-0.80% of Si; 0.001-0.200% of C; 0.05-0.20% of O; and 0.3-2.0% in total of at least one kind selected from the group consisting of Nb and Ta; and optionally, 0.005-0.200% of B; 0.2% or less of N; 0.2% or less of Fe; 0.2% or less of Ni; and 0.2% or less of Cr; 0.005-0.200% of B; 0.2% or less of N; 0.2% or less of Fe; 0.2% or less of Ni; and 0.2% or less of Cr; with the balance being Ti and unavoidable impurities, a first heat treatment step in which the alloy is heated and held at a temperature that is within a β-single-phase temperature region and is higher than a β transformation point T β, an adjustment forging step in which the alloy is hot-forged at a temperature that is within an (α+β)-two-phase temperature region and is lower than the β transformation point T β, thereby adjusting an equiaxed α phase, a second heat treatment step in which the alloy is heated and held at a temperature that is within the (α+β)-two-phase temperature region and is higher than the temperature in the adjustment forging step, followed by cooling to precipitate an acicular α phase, and an aging heat treatment step which is performed at 570-650°C, wherein, prior to the first heat treatment step, the alloy is subjected to a pre-forging step in which the alloy is hot-forged in the β-single-phase temperature region and further hot-forged in the (α+β)-two-phase temperature region, whereby the acicular α phase is formed in the β-grains, and the equiaxed α phase has an average grain diameter of 5 μm to 20 μm and an average aspect ratio of 5.0 or less and is contained in an amount of 5-35% in terms of sectional areal proportion to the composite structure, wherein the pre-forging step is a step in which the alloy is hot-forged in the β-single-phase temperature region and further hot-forged in an (α+β)-two-phase temperature region of [(T β -100°C) or higher and lower than T β] so as to result in a total forming ratio in the forging of 3 or higher.