We have developed the composite long afterglow phosphors for the phosphorescent thermo-sensor application. The mixture of SrAl2O4:Eu,Dy (SAO) and CaAl2O4: Eu,Nd (CAO) was chosen and examined as a thermo-sensor material. The mixture of SAO and CAO shows the broad PL spectra centered at the wavelength of about 510 nm and 440 nm originating from the 5d-4f transition in Eu2+ ions doped in the host crystals. The photoluminescence (PL) intensities at 510 nm and 440 nm have different temperature dependence for the temperature from 300 K to 500 K. It has been clarified that the temperature dependence of the PL intensity ratio of 510 nm and 440 nm directly shows the actual temperature without processing calibration of the temperature. Moreover, the compositional volume ratio of the CAO and SAO is optimized to be CAO/SAO = 2 in order to realize a high sensitive and accurate temperature measurement for the thermo label application of the phosphorescent composite. (C) 2011 The Electrochemical Society. [DOI: 10.1149/2.011112jes] All rights reserved.