This paper deals with the thermal performances of PCM/diatomite composites for energy saving. The PCM/diatomite composites were prepared by incorporating PCMs in the pores of diatomite to increase the form stability of PCMs. In experiment, we used n-hexadecane, n-octadecane and paraffin wax as PCMs, which have latent heat capacities of 254.7 J/g, 247.6 J/g and 144.6 J/g, respectively; and melting points of 20.84 degrees C, 30.4 degrees C and 57.09 degrees C, respectively. The PCMs could be retained at 50 wt% in the pores of the diatomite without leakage. The thermal effect of vacuum impregnation was also analyzed through vacuum treatment during the preparation process of samples. An optimal preparing method for 50 wt% of PCM impregnation is proposed. Thermal properties of samples were determined using DSC and TGA. And SEM and FTIR analyses were carried out to analyze microstructure and chemical properties of samples. SEM results showed that the PCMs are well-infiltrated into the structure of diatomite. DSC analysis results showed that the latent heat capacities of PCM/diatomite composites were 50% the value of pure PCMs, and TGA analysis results showed that PCM/diatomite composites have greater thermal durability compared with pure PCM. (C) 2013 Elsevier Ltd. All rights reserved.