The structure and magnetic properties of Pr2(Fe1-xCox)17-yGay compounds with 0≤x≤1 and 0≤y≤3 have been investigated using x-ray diffraction (XRD) and magnetization measurements. XRD patterns demonstrate that all samples were single phase with the rhombohedral Th2Zn17-type structure, except for Pr2Fe16.5Ga0.5 with some impurity phases. The replacement of (Fe, Co) by Ga results in an approximately linear increase in the unit cell volume, and decrease in the Curie temperature and saturation magnetization. The substitution of Co for Fe leads to a nonlinear variation in the unit cell volume, the Curie temperature and the saturation magnetization. The magnetic anisotropy phase diagrams of Pr2(Fe1-xCox)16.5Ga0.5 (0≤x≤1) and Pr2(Fe0.4Co0.6)17-yGay (0≤y≤3) compounds have been determined from the temperature dependence of magnetization and the XRD patterns of magnetically oriented powder samples. Most of the samples exhibit easy plane anisotropy. A small range exists in the magnetic anisotropy phase diagrams of Pr2(Fe1-xCox- )17-yGay compounds at 300 K, in which the c axis is the easy magnetization direction, however, small amounts of Ga close the easy c-axis region at y=1.5. The spin-reorientation temperature was found to increase with Co and Ga content for Pr2(Fe1-xCox)16.5Ga0.5 (0.5≤x≤1) and Pr2(Fe0.4Co0.6)17-yGay (0≤y≤1.5) compounds, respectively. The relationship of the magnetocrystalline anisotropy with the lattice parameters and other magnetic properties were analyzed. © 1998 American Institute of Physics.