A new chemosensor based on the spirolactam form of rhodamine 101 hydrazone (III) is found to exhibit a reversible colorimetric response toward Cu2+ in aqueous solutions in a selective, sensitive and rapid manner because of a formation of a Cu(II)-III complex. The dominating absorption maximum at 584 nm is uniquely red-shifted among rhodamine chemosensors toward Cu2+. The fluorescence of III can be detected in a low concentration of Cu2+. The results revealed that III is a good colorimetric sensor to Cu2+ in the red region.