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 [Ln78Ni64(62)Si6] (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 (-Δ Sm) of 40.63 J kg-1 K-1 at 3.0 K at 7 T.