Abstract: Heat treatement processes with different solid-solution and aging temperatures were carried on Ti55531 titanium alloy bar and forging,and the effects of heat treatment processes on microstructure and tensile properties were studied. Results show that, with the increase of solid-solution temperature from 575 ℃ to 650 ℃, primary α phase in bar changed from granulated shape to strip or short bar-like, and until to change to β grains. The tensile strength and yield strength at room temperature obviously increased, the elongation and reduction of area dropped sharply with the increase of solid-solution temperature. With the decrease of aging temperature, the strip or short bar-like α phase gradually dissolved and precipitated with granulated shape, and tensile strength and yield strength at room temperature obviously increased and elongation and reduction of area sharply decreased. In order to obtain a best match between strength and plasticity for the bar, the solid-solution temperature should below the phase transition point and aging temperature within the range of 600 ℃ to 620 ℃. Strength and plasticity of the forging could meet the requiements of relavant standard when the solid solution temperature was below phase transition point and aging temperature was 600 ℃.