1-(1-(3-oxo-3H-benzo[f]chromen-2-yl)ethylidene)thiosemicarbazide (OCETSC) and its La(III) complex was synthesized, the characterization was disbursed by elemental analysis, IR, UV–Visible, mass, magnetic measurement and molar conductance techniques. Data interpretation of the La(III) complex indicates that the complex was formed with a stoichiometric ratio of 1:2 (La: ligand). The studied ligand act as a bidentate ligand by using both azomethine nitrogen and thiol sulfur as monoanionic center of donation. The theoretical conformational structure analyses were performed using density functional theory (DFT) for ligand and complex at B3LYP functional with 6-31G(++)d,p basis set for ligand and LANL2DZ basis set for the complex. The charge distribution within the ligands and its La(III) complex was calculated using Mulliken population analysis of (MPA) and natural population analysis (NPA). The antibacterial activity of the prepared compounds was tested against some kinds of Gram-positive and negative bacteria. Molecular docking investigation proved that the ligand and complex had interesting interactions with active site amino acids of ribosyltransferase (code: 3GEY).