Pure, C-coated and Co-doped LiFePO4 were prepared by the hydrothermal method. X-ray diffraction patterns showed no impurity phase after carbon coating and Co doping. Thermal effect and phase stability of the three samples as a function of irradiation power density were systematically studied by means of Raman spectroscopy. The correlations between the power density of the excitation laser and the surface structure were accurately established and compared. Results show that the features of highest phase stability, excellent thermal stability and the most sensitive to power density were displayed in the samples of pure, C-coated and Co-doped LiFePO4, which were mainly ascribed to the grain size, thermal conductivity and degree of order of the olivine structure, respectively. The results also indicate that particular attention should be paid in characterizing the structure and component of the material surface by Raman spectroscopy, where the thermal effect of laser irradiation will possibly alter material surface and thus induce wrong conclusions. Copyright © 2011 John Wiley & Sons, Ltd.