Magnetization measurements of single-crystal β phase hydrides RCo5H∼3 with R ≡ La, Ce and Nd have been carried out in high magnetic fields up to 40 T. The uniaxial Co magnetocrystalline anisotropy becomes about half of that in the parent compounds upon hydrogenation, which is related to the decrease in the Co moment. The uniaxial contribution from the Ce sublattice in the parent compound almost vanishes upon hydrogenation. The magnetocrystalline anisotropy of the Nd sublattice and the NdCo intersublattice exchange interaction become lower than those in the parent compounds, resulting in a significant reduction of the spin reorientation temperature.