Phase change materials (PCMs) have been extensively integrated with ventilated walls to improve their thermal performance and the indoor thermal comfort, and the optimal PCM could gain the best improvement. However, there were few studies on the optimal PCM incorporated into ventilated walls. To accurately obtain the optimal PCM, a series of numerical models, including indoor air, soil and an active-passive ventilated wall with PCM, were developed and validated by an experiment. Then both phase change temperature and heat of fusion of PCM were changed and written into the developed models, and their effect on different performance indicators, namely heat storage density, heat storage efficiency and minimum indoor air temperature, was discussed. Finally, the optimal PCM was determined with different objectives, and potential PCMs were recommended. The results showed that the change trend of the optimal heat of fusion of PCM was opposite with different with different objectives, but the relationship between the optimal phase change temperature and the optimal heat of fusion was fitted into a curve. With the multiple objectives of maximizing all of the proposed performance indicators, the optimal PCM was at the connection point between the minimum indoor air temperature curve and the relationship fitting curve. (C) 2019 Elsevier Ltd. All rights reserved.