Inclusion interaction of β-cyclodextrin (β-CD) and 6-mono- (N-aminoethyl) amino-β-cyclodextrin (9-CDen) with congo red and interaction of congo red (CR) and inclusion complexes β-CD/CR and β-CDen/CR with calf thymus DNA are researched by UV-vis and fluorescence spectra. The results show that the values of the binding constants (Kb) of CR/ DNA, CR-β-CD/DNA and CR-β-CDen/DNA are 4.1 × 10^4 L/tool, 1.36 × 10^5 L/mol and 2.33× 10^5 L/mol respectivly, which indicates that the interaction between CR-β-CDen and DNA is the stronges...