Hydrogen solubility (S(10^-2cm³g^-1atm^-0.5)) in Al-(0-50mass%) Cu alloys were measured by a desorption technique for the thermally gas-charged cylindrical samples which were solidified unidirectionally in the pure nitrogen gas flow (sample ND). The solubility was compared with that in samples melted and cast in vacuum (sample VM) and with that in samples melted in air and cast into a metal mould (sample AM). Since the solubility S (ND) was almost equal to S(VM), samples ND were found to have no voids of gas defects such as porosity and cavity. In the region of α-solid solution (Cu<5.7mass) S (ND) was independent of copper content, therefore, the hydrogen solubility in the α-solid solution with the maximum Cu solubility (Cu=5.7mass%) was equal to that of pure aluminum (Sα=S (Al)). When the copper concentration was higher than 5.7mass%, S (ND) increased linearly with the increase in the volume fraction of the θ-phase (f_θ) and got to the higher hydrogen solubility in the θ-phase (S_θ), according to the equation S (ND)=Sα(1-f_θ)+S_θf_θ. S (AM) was greater than S (ND) due to the trapped hydrogen gas in the voids. In the alloy of teh eutectic composition (33 mass%Cu) which had little voids, S (33AM) was smaller than S (33ND). This was attributed to a non-equilibrium or suppressed charging of hydrogen due to the trapping of hydrogen in a finer metallic structure of a sample AM.