Peri-urban area has long served as a natural flood protection tool. However, in recent years, the city of Phnom Penh has been rigorously reclaimed for urban land use, and urban flooding has increased exponentially. The peri-urban area has the potential to formally serve as a stormwater management asset for the whole metropolitan. This study investigates the flood control potentiality of the peri-urban area in Phnom Penh, Cambodia, through flood susceptibility mapping and determines its flood control factor. It also reveals the suitable peri-urbanization pattern that allows for intense urban development while continuing to provide flood protection.