The magnetic and magnetocaloric properties of （Tb1-xDyx）6Co1.67Si3 （0 ≤ x ≤ 0.8） have been experimentally investigated. The compounds exhibit a Ce6Ni2Si3-type hexagonal structure and undergo a second-order magnetic transition. The Curie temperature decreases from - 187 K to 142 K as the content of Dy grows from 0 to 0.8. The maximal magnetic entropy change, for a field change of 0-5 T, varies between - 6.2 and - 7.4 J/kg.K, slightly decreasing when Dy is introduced. The substitution of Dy leads to a remarkable increase in refrigeration capacity （RC）. A large RC value of - 626 J/kg is achieved for x = 0.4 under a field change of 0-5 T.
