By the anionic template strategy, we have, for the first time, succeeded in introducing SiO44- into 3d-4f huge clusters, obtaining two novel nanosized clusters with interesting nanosized cores of [Ln(78)Ni(64(62))Si(6)] (1, Ln = Gd; 2, Ln = Eu). To the best of our knowledge, they are the largest heterometallic clusters incorporated with Si-O tetrahedra. In addition, compound 1 shows a maximum magnetic entropy (-Delta S-m) of 40.63 Jkg(-1) K-1 at 3.0 K at 7 T.