This paper experimentally and numerically investigated the thermal performance of cementitious composites containing polystyrene/n-octadecane microcapsules (MPCM-CCs). The focus was placed on the passive cooling and heating, and the peak load reduction and shifting of MPCM-CCs subjected to extreme temperature conditions (10-50 degrees C). Adding microcapsules with a latent heat of 142.9 J/g effectively improved the heat storage and thermal insulation performance of MPCM-CCs, thereby mitigating the temperature fluctuations of inner surface and indoor air by up to 17.5 degrees C and 10.7 degrees C, respectively. The peak load was reduced and shifted by up to 260 W/m(2) and 675 s in the heating process (1130 s), and 436 W/m(2) and 465 s in the cooling process (1750 s). Further, this study evaluated the influence of differential scanning calorimetry (DSC) scanning rate on the phase change properties of microcapsules and the consistency between the simulation and experimental results of MPCM-CCs. Due to the low thermal conductivity of polystyrene shell, the phase change temperatures of microcapsules varied significantly with DSC scanning rates. Consequently, the simulation results based on improper scanning rates deviated from the experimental results, which highlights the importance of considering the difference between the temperature change rates of building components and DSC analysis. (C) 2021 Published by Elsevier Ltd.