Abstract: In this study, the fatigue crack growth rate (FCGR) of a Ti–15V–3Cr–3Al–3Sn (Ti-15-3) alloy, which was aged at a temperature range of 371 to 593°C, was measured in air at room temperature. The specimen aged at 371°C showed clear serrations in the crack growth curve at a stress ratio (R) of 0.1, and it also exhibited a larger Paris law gradient than the other aged specimens at R = 0.5. The peak-aged (426°C aged) specimen had the highest FCGR of the specimens, regardless of the stress ratio. A gradual decrease in the FCGRs with increasing aging temperature, from 482 to 593°C, was observed for the over-aged specimens. Cleavage-like fracture was more likely to occur in the under- and peak-aged specimens as compared to the transgranular fatigue in the over-aged specimens. It seemed that the coarse α platelets with lowered hardness in the over-aged specimens resulted in a higher resistance to fatigue crack growth in the Ti-15-3 alloy.