The molecular recognition of cucurbit［7, 8］urils toward a methylene blue dye was investigated by using electronic absorption spectroscopy and fluorescence spectroscopy. The experimental results revealed that the formation of host-guest complexes between Q［7］ and the methylene blue dye were formed with a stoichiometry of 2∶1, while the formation of host-guest complexes between Q［8］ and the methylene blue dye were formed with a stoichiometry of 1∶2. The calculated binding constants are KQ［7］-g=1.34×1012 L2·mol-2 and KQ［8］-g=5.34×1012 L2·mol-2 respectively based on the absorption spectrophotometric analysis, while the calculated binding constants are KQ［7］-g=1.53×1012 L2·mol-2 and KQ［8］-g=6.11×1012 L2·mol-2 respectively based on the fluorescence spectroscopy analysis. The values of K are reasonably consistent. The fluorescence of the guest was found to rapidly increase with the increase in the concentration of Q［7］, while the fluorescence of the guest was found to rapidly decrease with the increase in the concentration of Q［8］. Based on the variation of the absoption or fluorecence of the host-guest complexes of Q［7］ or Q［8］-methylene blue dye with the variation of pH, the interaction of the Q［7］ or Q［8］ and the methylene blue dye with an unchangeable ratio can be observed in the range of pH between 0.5 and 13.