The interaction of hematoporphyrin dihydrochloride (HD) with DNA was studied by using neutral red (NR) as a probe.The results indicate that a super-molecule complex of HD and DNA is produced, which has been confirmed by absorption and fluorescence spectra.The binary complex ratio of nHD∶nDNA is 3∶1, and the binding constant of HD interacting with DNA is 1.84×104 L/mol. The interaction of HD with DNA is studied. The results suggest that the mingling mode is the major mode for interaction between HD and herring sperm DNA. The mechanism is probably partial intercalation binding with covalent and electrostatical bindings. This interaction mode affects the distribution and expression of gene and resists the growth of cancer cells.