A water soluble spironaphthoxazine (SPO) was synthesized, and its spectral properties were determined. Under UV irradiation, colorless SPO shows intensive blue color while the intensity of its initial fluorescence decreased. In addition, SPO also exhibited high sensitivity to pH stimuli both in colorimetry and fluorometry distinguishing from the spectral appearance observed under UV irradiation. Further, integrating these two optical characteristics a three-state switching system can be established, and all interconversions can be observed by naked-eye.