Chemical introduction and release of fluorescent chromophores on a surface of Super-Paramagnetic Iron Oxide Nanoparticles (SPION) were investigated. An aqueous solution of SPION having carboxylic acid and poly(ethylene glycol) groups on its surface was prepared by a reported method. A fluorescent chromophore, a derivative of fluorescein attached with aminobutenyl ether, was introduced into the SPION surface through amide bond by using of EDC. An emission of the fluorescein was quenched by introduction of the aminobutenyl ether, and the SPION solution introduced by the fluorescein derivative exhibited only weak fluorescence at ~510 nm. Once Pd(PPh<SUB>3</SUB>)<SUB>4</SUB> was added to the solution, butenyl ether bond was cleaved and release of free fluorescein was observed by increase of emission at 510 nm. This release reaction was also revealed by NMR and UV spectra of model compounds.