Seven hexacoordinated cis-dioxidomolybdenum(VI) complexes [MoO2L1–7] (1‐7) derived from various tetradentate diamino bis(phenolato) “salan” ligands, N,N′-dimethyl-N,N′-bis-(2-hydroxy-3-X-5-Y-6-Z-benzyl)-1,2-diaminoethane {(X = Br, Y = Me, Z = H (H2L1); X = Me, Y[dbnd]Cl, Z = H (H2L2); X = iPr, Y = Cl, Z = Me (H2L3)} and N,N′-bis-(2-hydroxy-3-X–5-Y-6-Z-benzyl)-1,2-diaminopropane {(X = Y = tBu, Z = H (H2L4); X = Y = Me, Z = H (H2L5); X = iPr, Y[dbnd]Cl, Z = Me (H2L6); X = Y = Br, Z = H (H2L7)} containing O‐[sbnd]N donor atoms, have been isolated and structurally characterized. The formation of cis-dioxidomolybdenum(VI) complexes was confirmed by elemental analysis, IR, UV–vis and NMR spectroscopy, ESI-MS and cyclic voltammetry. X-ray crystallography showed the O2N2 donor set to define an octahedral geometry in each case. The complexes (1–7) were tested for their in vitro antiproliferative activity against HT-29 and HeLa cancer cell line. IC50 values of the complexes in HT-29 follow the order 6 < 7 << 1 < 2 < 5 << 3 < 4 while the order was 6 < 7 < 5 < 1 << 3 < 4 < 2 in HeLa cells. Some of the complexes proved to be as active as the clinical referred drugs, and the greater potency of 6 and 7 (IC50 values of 6 are 2.62 and 10.74 μM and that of 7 is 11.79 and 30.48 μM in HT-29 and HeLa cells, respectively) may be dependent on the substituents in the salan ligand environment coordinated to the metal. © 2017 Elsevier Inc.