Abstract: Ti6242S titanium alloy large bars were processed by solution-aging and annealing treatment. The effect of the sizes of the treated specimens on microstructure and mechanical properties as well as ultrasonic flaw detection was studied. The results indicated that the primary α content increased near the center for the STA specimen,and equiaxed α-phase content was higher in annealed microstructure than that in solution-aged microstructure; the creep resistance of Ti6242 S titanium alloy annealed was poor; the overall property was better by solution-aging treatment; uniformity of the ultrasonic flaw detection bottom wave on the alloy large bar solution- aged increased slightly,while ordinary annealing treatment brought no such effect.