In　this　paper,　the　synthetic　route　of　a　potential　antitumor　reagent,　benzo[b][1,10]　phenanthrolin-7(12H)-one　(BPO),　was　improved.　A　sulfonic　group　was　introduced　to　BPO　to　form　a　new　compound,　7-oxobenzo[b][1,10]phenan-throline-12(7H)-sulfonic　acid　(OPSA),　in　order　to　enhance　its　water-solubility.　The　molecular　structure　of　OPSA　has　been　confirmed　by　IR,　UV,　MS,　1H　NMR　and　elements　analysis.　It　was　proved　in　our　experiments　that　DNA　could　quench　the　fluorescence　of　OPSA　and　the　maximum　quenched　intensity　appeared　at　408　nm　(λex　=　284　nm).　The　quenched　fluorescence　intensity　was　proportional　to　the　concentration　of　DNA.　Based　on　this　phenomenon,　OPSA　had　been　used　as　the　fluorescent　probe　for　detection　of　calf　thymus　DNA　(ct-DNA)　and　the　corresponding　linear　response　range　was　from　1.0　to　150.0　μg　mL-1　and　the　limit　of　detection　(LOD)　was　3.8　ng　mL-1.　Its　interaction　with　ct-DNA　was　investigated　by　fluorescence,　absorption　and　viscosity　measurements.　When　binding　to　ct-DNA,　OPSA　showed　obvious　fluorescence　quenching　and　the　quenched　intensity　was　stable　with　the　presence　and　absence　of　NaCl.　The　absorption　spectra　of　OPSA　had　no　evidence　of　increasing　or　decreasing　when　ct-DNA　was　added.　The　viscosity　of　OPSA　and　ct-DNA　mixture　showed　no　obvious　change　comparing　with　the　viscosity　of　ct-DNA　along.　The　results　suggested　that　the　interaction　between　OPSA　and　ct-DNA　was　groove　binding　in　nature.　Scatchard　plots　constructed　from　fluorescence　titration　data　gave　a　binding　constant　of　8.9　×　105　L　mol-1　and　a　binding　site　size　of　0.35　base　pairs　per　bound　drug　molecule.　©　2007.