We proposed a competitive method for rapid and sensitive detection of spermine using CB[7]-PHE (CB[7] = cucurbit[7]uril, PHE = phenazopyridine) as a platform. The LOD was determined to be 21nM and showed good calibration in the concentration range of 0.071-14 mu M, which is sufficiently below the critical concentration for cancer diagnosis. More interestingly, the addition of spermine to CB[7]-PHE led to color change from light brown to yellow, which indicating potential applications for colorimetric analysis of spermine.