The interaction between calf thymus DNA (ctDNA) and Pd (Ⅱ) meso-tetralds- (4-N-methyl pyridiniumyl) porphyrin (Pd-TMPyP) was investigated by steady solid-substrate room temperature phosphorescence (SS-RTP). The SS-RTP intensity and lifetime of Pd-TMPyP enhanced with the increasing ctDNA. The anion quenching experiment of Pd-TMPyP indicated that Pd-TMPyP intercalated into ctDNA, which was also approved by UV-Vis spectra. Keywords: Pd-TMPyP, ctDNA, SS-RTP, intercalation