ABSTRACTFatigue crack growth rates (FCGR) of the inertia friction welded Ti17 alloy joint was studied at room temperature (RT) and 400 °C at a stress ratio of 0.1. Microstructural analysis and mechanical tests were also carried out. The results show that at RT, FCGR of weld metal with recrystallisation microstructure was higher compared with the base metal and the thermo‐mechanically affected zone. At 400 °C, however, the difference of the FCGR became insignificant. Fractographic observation showed that the failure of the base metal was dominated by slip band in transgranular mode at both RT and 400 °C, whereas crack in weld metal grew in intergranular mode at RT but in transgranular mode at 400 °C. The combined effects of lower yield strength and bigger yield‐ultimate tensile strength difference may be responsible for the higher fatigue crack growth (FCG) resistance of inertia friction welded Ti17 alloy at elevated temperature.