Abstract Terminal solubility and partitioning of hydrogen in Zr–Nb alloys with different niobium concentrations were examined using differential scanning calorimetry and hot vacuum extraction mass spectrometry. Specimens were charged to different concentrations of hydrogen and annealed at 1123 K to generate a two-phase structure consisting of α-Zr (Zr–0.6 wt.% Nb) and metastable β-Zr (Zr–20 wt.% Nb) within the alloy. Specimens were aged at 673 and 773 K for up to 1000 h to evaluate the effect of the decomposition of the metastable β-Zr to α-Zr+β-Nb on the solubility limit. The results show that the solubility limit for hydrogen in the annealed Zr–Nb alloys is higher than in unalloyed Zr and that the solubility limit increases with the niobium concentration of the alloy. They also show that the hydrogen solubility limits of the completely aged Zr–Nb alloys are similar and approach the values for pure α-Zr. The solubility ratio of hydrogen in β-Zr (Zr–20 wt.% Nb) to that in α-Zr (Zr–0.6 wt.% Nb) was found to range from 9 to 7 within the temperature range 520–580 K.