In the study on the reactivity of tetraselenomolybdate, a DMF solution of [Et4N](2)[MoSe4] was found to react with 3 equiv of CuCl in the presence of NaS2CNR2 [R-2 = Et-2, C5H10, (PhCH2)(2), Me-2] to give a series of Mo-Cu-Se compounds, [Et4N](2)[MoCu3Se4(R2NCS2)(3)] (R-2 = Et-2 (1a), C5H10 (1b), (PhCH2)(2) (1c)) and [Et4N](2)[MoCu4Se4(Me2NCS2)(4)] (2). Furthermore, the reaction of 2 or [Et4N](2)[MoSe4(CuCN)(2)] with [Et4N](2)[Cu(SPh)(3)] in DMF/MeCN afforded a polynuclear Mo-Cu-Se cluster compound, [Et4N](4)[MoCu10Se4(PhS)(12)] (3). [Et4N](2)[MoCu3Se4(Et2NCS2)(3)] (la) crystallizes in the orthorhombic space group P2(1)2(1)2(1) With cell dimensions a = 12.949(3) Angstrom, b = 13.339(3) Angstrom, c = 29.744(6) Angstrom, V = 5137.6 Angstrom(3), and Z = 4. Full anisotropic refinements of the structure led to convergence with a value of R = 0.052 (R-w = 0.055) for 453 variables and 6854 reflections (F > 4.0 sigma(F)). The [MoCu3Se4(Et2NCS2)(3)](2-) anion in la comprises three Et2NCS2Cu fragments linked by a slightly distorted tetrahedral MoSe4 moiety. Compound 2 crystallizes in the orthorhombic space group Pbca with cell constants a = 14.600(3) Angstrom, b = 18.765(4) Angstrom, c = 37.781(8) Angstrom, V = 10351 Angstrom(3), and Z = 8. Anisotropic refinements with 5328 reflections (F > 4.0 sigma(F)) and 460 parameters for all non-hydrogen atoms yielded the values of R = 0.075 and R-w = 0.080. The [MoCu4Se4(Me2NCS2)(4)](2-) anion structure of 2, which possesses a pseudo D-2d symmetry of the MoSe4Cu4 core and a nearly planar MoCu4 array, consists of four Me2NCS2Cu fragments coordinated across four edges of the tetrahedral [MoSe4](2-) moiety. The compound [Et4N](4)[MoCu10Se4(PhS)(12)] (3) crystallizes in the tetragonal space group with cell dimensions a = 18.344(3) Angstrom, c = 18.368(4) Angstrom, V = 6180.9 Angstrom(3), and Z = 2. A value of R = 0.079 (R-w = 0.084) for 218 parameters and 3314 observations (F > 4.0 sigma(F)) was obtained from anisotropic refinements of the non-hydrogen atoms. The [MoCu10Se4(PhS)(12)](4-) anion structure of 3 can be described as six Cu atoms bonded across the six edges of a central MoSe4 tetrahedron, forming an octahedral MoSe4Cu6 array, to which the other four Cu atoms are added in a tetrahedral array bridged by 12 mu-SPh ligands. The Mo-95 NMR spectra of the all compounds in DMF show a single resonance peak. Their chemical shifts are dependent on the deshielding effect from the number of the Cu atoms around Mo atom and the structures of the compounds. The H-1 NMR, IR, and electronic spectroscopic data of these compounds are also consistent with their solid-state structures.