Abstract: Mica was used as a supporting matrix for composite phase change materials (PCMs) in this work because of its distinctive morphology and structure. Composite PCMs were prepared using the vacuum impregnation method, in which mica served as the supporting material and polyethylene glycol (PEG) served as the PCM. Fourier transform infrared and X-ray diffraction analysis confirmed that the addition of PEG had no effect on the crystal structure of mica. Moreover, no chemical reaction occurred between PEG and mica during the vacuum impregnation process, and no new substance was formed. The maximum load of mica-stabilized PEG was 46.24%, the phase change temperature of M₄₀₀/PEG was 46.03°C, and the latent heat values of melting and cooling were 77.75 and 77.73 J·g⁻¹, respectively. The thermal conductivity of M₄₀₀/PEG was 2.4 times that of pure PEG. The thermal infrared images indicated that the thermal response of M₄₀₀/PEG improved relative to that of pure PEG. The leakage test confirmed that mica could stabilize PEG and that M₄₀₀/PEG had great form-stabilized property. These results demonstrate that M₄₀₀/PEG has potential in the field of building energy conservation.