Abstract: In this paper, the long term stability of porous media based phase-changing composites is investigated by means of fourier transformation infrared spectrum analysis (FTIR). The infrared spectra of lauric acid contained in the phase-changing composites that underwent more than one year of phase-changing cycles were tested and analyzed in comparison with those of sodium laurate and pure lauric acid which did not undergo any phase-changing cycle. The results show that all absorption peaks of the functional groups and chemical bonds of lauric acid still exist, which suggests that the chemical structure of lauric acid did not change after such a long time of phase-changing process in porous media. So it is concluded that the lauric acid, as organic phase-changing material, is chemically compatible with the porous media, and the phase-changing composites have long term chemical stability.