Abstract: The determination of grain size for various titanium alloys was defined. The grain size of α,β titanium alloys was determined by the comparison method and intercept procedure in GB/T 6394-2017. The methods of grain size determination for equiaxed microstructure, duplex microstructure, basketweave microstructure, widmanstatten, non-equiaxed microstructure and ultrafine grain microstructure in α-β two-phase titanium alloys were studied. The results show that comparison method and intercept procedure in GB/T 6394-2017 can be used to determine the grain size of α and β single-phase titanium alloy, α-β two-phase titanium alloy with definite phase content and ultrafine grain microstructure after recrystallization heat treatment.