Abstract A novel ligand 2-acetyl-2-thiazoline acetylhydrazone (ATHAc) and two new chloride-bridged dimeric nickel(II) complexes containing thiazoline hydrazone derivative ligands, [{Ni(ATsc)(MeOH)}2(μ-Cl)2]Cl2 (1) (ATsc = 2-acetyl-2-thiazoline semicarbazone) and [{Ni(ATHAc)(H2O)}2(μ-Cl)2]Cl2 (2), were prepared and structurally characterized by elemental analysis, single crystal X-ray diffraction, IR and UV–Vis spectroscopy. In addition, NMR spectroscopy for ATHAc and magnetic susceptibility measurements for nickel complexes were performed. The structure of nickel(II) complexes consists of dimeric molecules in which nickel ions are bridged by two chloride ligands. The coordination geometry around each nickel ion can be described as a distorted octahedron with each nickel atom coordinated to one thiazoline nitrogen atom, one imine nitrogen atom, one carbonyl oxygen atom, one oxygen atom (from a methanol molecule in 1 and from a water molecule in 2) and two bridge chloride ligands. The variable temperature magnetic susceptibility measurements of the complexes show the ferromagnetic behaviour in the solid state (J = 5.7(2) cm−1 in 1; 6.6(3) cm−1 in 2).