A new concept of using luminescent nanoparticles for thermometry is described in this paper. To demonstrate this idea, the temperature-dependent emission characteristics of several luminescent nanoparticles have been investigated. The results show that some of them have a linear response above room temperature, which could be applied to temperature sensing. Semiconductor nanoparticles of CdTe and doped nanoparticles of ZnS:Mn2+ show a reversible linear temperature response over the physiological temperature range and have potential for biomedical thermometry. Double-doped nanoparticles of ZnS:Mn2+,Eu3+ show a different temperature response for each dopant; the ratio of their intensities provides a robust temperature measurement approach. Thermal instability of the nanoparticle stabilizer and nanoparticle surface defects is a possible reason for the irreversible thermal response of some nanoparticles.