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 φ = DKs. It is found D = 1.52 × 10-6exp(-54100/RT), Ks = 2.2 × 10-6exp(-5400/RT) and φ = 3.3 × 10-12exp(-59500/RT) for hydrogen,where Ks (Sieverts’ constant) is given in Pa-1/2, D in m2·s-1·Pa-1/2, T in K and R=8.31J·mol-1·K-1. By taking isotope effects into account, the corresponding Arrhenius relations for deuterium and tritium are also deduced.