Based on a study of the phase relation in the Fe- and Co-rich region of the equi-gadolinium content section with the Gd content corresponding to the chemical formula Gd3(Fe,Co,Cr)29 in the Gd-Fe-Co-Cr quaternary system, formation, structure and magnetic properties of the 3∶29-type Gd3(Fe1-xCox)29-yCry compounds have been investigated. It has been found that the composition range of formation of the single phase Gd3(Fe1-xCox)29-yCry Compounds is 0≤x≤0.7 for y=5.0, 0.7≤x≤0.8 for y=5.5, and 0.8≤x≤1.0 for y=6.0. A pure Co-based Gd3Co29-xCrx compound series have been synthesized. The solubility limit of the Cr atoms in the Gd3Co29-xCrx compounds was found to be from x=6.5 to x=7.3. The results indicate that all the synthesized Gd3(Fe1-xCox)29-yCry compounds crystallize in Nd3(Fe,Ti)29 type structure of the monoclinic system and the space group A2/m.The solubility limit of Co atoms in the Gd3(Fe1-xCox)29-yCry compounds increases with increasing the stabilizing element Cr. It is noteworthy that substitution of Co for Fe leads to a remarkable change of the magnetocrystalline anisotropy of the Gd3(Fe1-xCox)29-yCry compounds. When x≥0.4 the anisotropy changes from the easy plane type to the uniaxial type, which is important for permanent magnet application.