Caprylic hydrazide ligands are ideal ligands for the synthesis of novel polynuclear metal complexes, because they contain many N,O coordination atoms with a strong coordination ability, abundant hydrogen-bond donors, acceptors, and large conjugation systems. Here, we successfully obtained one dodecanuclear cobalt nanocluster [CoII8CoIII4(L1)4(Py)12(CH3OH)4(CH3COO)4]·(CH3OH)13 (1) and one octadecanuclear cobalt nanocluster [CoII18(L2)6(Py)48]·(DMF)5·(CH3OH)8 (2) by using H6L1 and H6L2 ligands, respectively (Py = pyridine; DMF = dimethylformamide). The cyclic cobalt nanocluster 1 can be regarded as two pentanuclear cobalt units (Co5(N-N)4) connected by two cobalt ions, and it is a mixed-valent Co nanocluster. Every H6L1 ligand contains 10 coordination atoms, each of which coordinates with the Co ions. And every two H6L1 ligands form a structure similar to a handshake. The abnormal cylindrical cobalt nanocluster 2 can be regarded six trinuclear cobalt units Co3(N-N)2 connected by one L26- ligand, and every L26- ligand splits the structure on both sides, with a twisted cyclohexane in the middle. AC magnetic susceptibilities show that nanocluster 1 exhibits no frequency-dependent behavior, but nanocluster 2 shows an obviously single-molecule magnetic behavior, and the relaxation process of the energy barrier is 20.4 K.