The structural and magnetic properties of YGdFe17_xCox Ga (x = 0,1, 2 and 3) have been investigated through X-ray diffraction and magnetization studies. All the compounds up to x = 0.2 are formed in a single-phase, hexagonal structure. The unit cell volume decreased with the addition of Co due to the smaller size of Co than that of Fe. The magnetization and Curie-temperature values are found to increase with the addition of x and could be due to the additional Co-Co, Fe-Co exchange whose magnitude is larger compared to that of Fe-Fe exchange. Magnetically aligned sample powders indicate the presence of planar anisotropy for all the compounds. © 2006 IEEE