A new ligand L, 1-[3-(2-pyridyl)pyrazol-1-ylmethyl]naphthalene, and its two metal complexes, [Cu(L) 3 ](ClO 4 ) 2 (1) and [Zn(L) 3 ](ClO 4 ) 2 (H 2 O) 2 (2), have been synthesized and characterized. The crystal structure of complex 1 was determined by single crystal X-ray diffraction, which crystallized in monoclinic, space group P2 1 /n with unit cell parameters, a=12.710(4) Å, b=12.135(3) Å, c=33.450(9) Å, β=93.281(5)° and Z=4. The Cu atom was six-coordinated to N(1), N(2), N(4), N(5), N(7) and N(8) from three L ligands and formed a slightly distorted octahedral geometry. Complexes 1 and 2, and ligand L were subjected to biological tests in vitro using three different cancer cell lines (HL-60, BGC-823 and MDA-MB-435). Complex 1 showed significant cytotoxic activity against three cancer cell lines. The interactions of complexes 1 and 2, and ligand L with calf thymus DNA were then investigated by thermal denaturation, viscosity measurements and spectrophotometric methods. The experimental results indicated that complexes 1 and 2 bound to DNA by intercalative mode via the ligand L. The intrinsic binding constants of complexes 1 and 2, and ligand L with DNA were 1.8×10 4 , 5.4×10 3 and 2.76×10 3 M −1 , respectively.