The magnetization has been measured for the singlecrystalline β-phase hydrides RCo5H∼ 3 with R  La, Ce and Nd in high magnetic fields up to 40 T. The Co magnetocrystalline anisotropy decreases by about 50% upon hydrogenation, which is related to the decrease of the Co moment. The uniaxial contribution from the Ce sublattice in CeCo5 almost vanishes in hydride. Magnetocrystalline anisotropy of the Nd sublattice and NdCo intersublattice exchange interaction become lower than those in NdCo5, resulting in the significant reduction of the spin-reorientation temperature.