In order to analyze the effect of cooling rate on lamellar morphology and mechanical properties during BASCA treatment in Ti5321 alloy, the lamellar morphology and mechanical properties of the titanium Ti5321 alloy under different BASCA treatment are comprehensively studied. The results show that the cooling rates have decisive influence on the alpha lamellar size formed at slow cooling process after β zone solution. The lamellar size of Ti5321 alloy keeps increase with the decrease of cooling rate, and the growth rate of lamellar in the length direction is much faster than that in the thickness direction. With the increase of cooling rate, the strength of the alloy is in-crease，but the fracture toughness decreases. The cooling rate of 0.5℃/min in this experiment is the optimal cool-ing way which the ultimate tensile strength of alloy can exceed 1200MPa with an excellent fracture tough-ness(KIC≥65MPa.m1/2).