Abstract: In this paper, by using an ingenious method, the hydrogen isotope solubilities and diffusivities in GWHER-1 stainless steel have been determined by a vacuum heating degassing approach at the temperature range of 597–1022 K on a set of specimens with different sizes previously charged for 24 h under a hydrogen isotope pressure of 10⁵ Pa in the temperature range of 800–1000 K. The permeabilities are then derived from the relation $\varPhi$ = DK_s. It is found D = 1.52 $\times$ 10^?6exp(?54100/RT), K_s = 2.2 $\times$ 10^?6exp(?5400/RT) and $\varPhi$ = 3.3 $\times$ 10^?12exp(?59500/RT) for hydrogen, where K_s (Sieverts' constant) is given in Pa^?1/2, D in m²$\cdot $s^?1$\cdot $Pa^?1/2, T in K and R=8.31J$\cdot$mol^?1$\cdot $K^?1. By taking isotope effects into account, the corresponding Arrhenius relations for deuterium and tritium are also deduced.