A new compound of azotetrazole-3-hydroxy-2-naphthoic acid (H₃ATNA) has been successfully synthesized and characterized. By controlling the ratio of metal ions to the ligand and the pH value of solution, mononuclear, dinuclear and tetranuclear dysprosium(III) complexes [Et₃NH]₃[Dy(HATNA)₃]·5H₂O (1), [Dy₂(HATNA)₃(DMF)(H₂O)]·2DMF·CH₃OH·2H₂O (2) and [Et₃NH]₆[Dy₄(ATNA)₆(H₂O)₂]·DMF·2CH₃CN·8H₂O (3) were synthesized and characterized by X-ray diffraction crystallography (DMF = N,N-dimethylformamide). Crystallographic data demonstrate that the neutral H₃ATNA exists as a hydrazone tautomer. Complex 1 is a mononuclear structure, in which the Dy(III) ion is a nine-coordinated ion surrounded by three tridentate HATNA⁻ ligands. Complex 2 shows a dinuclear structure, which is bridged by three μ_1,1-hydroxyl groups of three HATNA⁻ ligands. In complex 2, the Dy(III)1 ion is a nine-coordinated ion surrounded by three tridentate HATNA⁻ ligands, while Dy(III)2 is an eight coordinated atom with three tridentate HATNA⁻ ligands, one DMF and one water molecule. Complex 3 displays a tetranuclear structure, which can be approximately considered as two μ_1,3-carboxyl groups of ATNA³⁻ ligands linking complex 2. The magnetic properties of 1–3 were investigated. Complexes 2 and 3 display slow magnetic relaxation in a zero dc field.