Using palmitic acid (PA) as an organic phase change material (PCM), a series of PA/diatomite composite PCMs (CPCMs) composed of PA absorbed into diatomite mesopores with different mass contents were made through direct impregnation method. Nitrogen adsorption-desorption curves indicated the porous structure of diatomite with the specific surface area and the mesopore peak at 40 m(2)/g and 3 to 5 nm, respectively. The form-stability measurement indicated that the maximum mass loading capacity of PA was 55 wt%. The melting temperature and fusion enthalpy of the PA/diatomite CPCM (55 wt%) were calculated from DSC at 63 degrees C and 88 J/g, respectively. The thermal cycle test implied that the PA/diatomite CPCM with 55-wt% PA loading showed excellent thermal reliability after 1000 thermal cycles. Moreover, the composite has thermal conductivity at 0.5810 W/m center dot K and enhanced thermal storage/release rate. PA/diatomite CPCM (55 wt% PA) was a suitable candidate for modern building energy saving and industrial solar energy.