In this paper, we have examined the structural, microstructural, and magnetic properties of Er-Co-B compounds. High-energy ball milling has been used to homogeneous the stoichiometric mixture of Er, Co and B as starting materials to synthesis the Er17Co75B8 powders. The samples are crystallized in the hexagonal CaCu5 - structure type with P6/mmm space group. Their structural and magnetic properties were assumed systematically as a function of annealing temperature. The structural properties were studied by means of X-ray diffraction and the microstructural properties via Scanning Electron Microscopy. The magnetic phase with abbreviated formula ErCo4.5B0.5 and global formula Er16.67Co75B8.33 was a dominate phase. These compounds exhibit a high coercivity of 8 kOe at room temperature for ErCo4.5B0.5 annealed at 1073 K for 1/2 h. These magnets with high H-C are appropriate to permanent magnet applications. We have also applied to the Approach of Saturation in to Magnetization (ASM). The results were understood in according to the model of random magnetic anisotropy.