To optimize the giant magnetocaloric properties of HoB2, we synthesized and characterized Ho1-xGdxB2 (0.1 ≤ x 0.4) alloys. We found out that Gd enters stoichiometrically randomly into Ho site, leading to a Vegard-type structural change. The addition spherical S7/2 Gd3+ moments prompts an enhancement in Curie temperature from 15 K 30 (at = 0.4), reduction peak value magnetic entropy change, 0.35...