The complex [Mn(L)(NO) (HO)] (1) (L52H-5-hydroxy-1, 2, 5-oxadiazo[3, 4-f]1,10-phenanthroline) was synthesized and character-3222 ized by elemental analysis, IR and UV. The crystal and molecular structure of 1 was determined by single-crystal X-ray diffraction; crystal data: light yellow, monoclinic, space group P2/n, Z54, a 57.432 (2) A, b59.582(3) A, c 523.445(7) A, b 590.519 (5)8. The Mn atom in 11 is hexa-coordinated in a distorted octahedral arrangement by two N atoms of the ligand L and four O atoms of two water molecules and two nitrate anions. Biological tests in vitro showed that 1 has significant antitumor activity against HL-60, KB, Hela and BGC-823 cells. The interaction of 1 with calf thymus DNA was investigated by absorption titration, thermal denaturation and viscosity measurements. The results suggest that 1 binds with DNA by intercalating via the ligand L.