Binary R₂Co₁₇ (R = rare earth metals except for La) intermetallic compounds show excellent magnetic properties and have potential application in high-temperature magnet; however, binary La₂Co₁₇ does not exist naturally, and its structure is expected to be stabilized via the design of high entropy at the La site. In this work, the high-entropy intermetallic compound (La_1/4Pr_1/4Nd_1/4Sm_1/4)₂Co₁₇ is designed and prepared using vacuum arc melting technology, and its crystal structure, elemental composition, and magnetic properties are systematically studied using X-ray diffraction, scanning electron microscopy with energy dispersive spectroscopy, and magnetic measurements. (La_1/4Pr_1/4Nd_1/4Sm_1/4)₂Co₁₇ is experimentally and theoretically confirmed to be a rhombohedral single phase with a configuration entropy of 11.52 J mol⁻¹ K⁻¹ at the La site. The high entropy can not only stabilize the La₂Co₁₇ phase but also improve the magnetic properties. The magnetic moment of (La_1/4Pr_1/4Nd_1/4Sm_1/4)₂Co₁₇ is 39.81 μ_B at 5 K, which is larger than the maximum value among the Pr₂Co₁₇, Nd₂Co₁₇, and Sm₂Co₁₇ compounds. In (La_1/4Pr_1/4Nd_1/4Sm_1/4)₂Co₁₇, the easy axis tends to be along the c axis with an anisotropy field of 17.25 kOe. It is suggested that the high entropy at the La site induces the change in the magnetic anisotropy from the basal plane to the easy axis in (La_1/4Pr_1/4Nd_1/4Sm_1/4)₂Co₁₇.