X-ray diffraction (XRD) and magnetization measurements were performed to investigate the effect of Ga substitution for Co on the structural and magnetic properties ofGd2Co17−xGaxcompounds(x=0,1, 2, 3, 4, 5, 6, 7, and 8). Crystal-structure studies indicate that all samples are single phase with the rhombohedralTh2Zn17-type structure except for the samples withx=7and 8, which contain a small amount of Co. The Ga substitution for Co inGd2Co17compounds leads to a monotonic increase in the unit cell volume and an approximately linear decrease in the saturation magnetization. The Curie temperatureTCis found to decrease monotonically from 1210 K forx=0to 30 K forx=8.The compensation points are observed for theGd2Co17−xGaxsamples withx=5and 6. The value of the compensation temperature, determined from the temperature dependence of the magnetization measured in a magnetic field of 1000 Oe, is 120 and 152 K forx=5and 6, respectively. It is noteworthy that the substitution of Ga for Co in theGd2Co17compounds has a remarkable influence on the magnetocrystalline anisotropy. XRD studies on magnetic-field orientedGd2Co17−xGaxpowders show that the sample withx=0exhibits an easy-plane anisotropy, while the samples withx⩾1exhibit an easyc-axis anisotropy at room temperature. The change of the easy magnetization direction ofGd2Co17−xGaxcompounds from a basal plane tocaxis indicates that the substitution of Ga for Co leads to the decrease of the planar anisotropy of the Co sublattice. ©1997 American Institute of Physics.