Five new transition metal molybdenum(VI) selenites or tellurites, namely, TM(MoO3)(SeO3)(H2O) = (TM = Mn, Co), Fe-2(Mo2O7)(SeO3)(2)(H2O), Cu-2(MoO4)(SeO3), and Ni-3(MoO4)(TeO3)(2), have been prepared and structurally characterized. They belong to five different types of structures. Mn(MoO3)(SeO3)(H2O) and Ni-3(MoO4)(TeO3)(2) are non-centrosymmetric and crystallize in the orthorhombic space groups Pmc2(1) and P2(1)2(1)2(1), respectively, whereas Co(MoO3)(SeO3)(H2O), Fe-2(Mo2O7)(SeO3)(2)(H2O), and Cu-2(MoO4)(SeO3) are non-centrosymmetric and crystallize in P (1) over bar, C2/c, P2(1)/c, respectively. The Mo6+ cations in Mn(MoO3)(SeO3)(H2O), Co(MoO3)(SeO3)(H2O), and Fe-2-(Mo2O7)(SeO3)(2)(H2O) are in severely distorted octahedral geometry whereas those in Cu-2(MoO4)(SeO3) and Ni-3(MoO4)(TeO3)(2) are in a slightly distorted tetrahedral geometry. Second-Harmonic Generation (SHG) measurements revealed that (MoO3)(SeO3)(H2O) displays a moderate SHG signal of about 3 x KH2PO4 (KDP) whereas the SHG response of Ni-3(MoO4)(TeO3)(2) is much weaker than that of KDP.