【Objective】Biodegradable plastic mulch films, which are representatively made from polybutylene adipate co-terephthalate (PBAT), have been widely used in the agricultural areas of northwest China. As a result, a large quantity of nanoplastics is left in the local soils. However, the effect of these nanoplastics on the properties of this predominantly clay soil remains understudied. 【Method】This study used clays separated from saline-alkaline soils from northwest China and PBAT-based biodegradable nanoplastics (PBAT-BNPs) as research objects. Clay rewetting was conducted to simulate the soil moisture changes during the agricultural irrigation period in Xinjiang. The effects of PBAT-BNPs on the aggregation behavior and physicochemical properties of sterilized high saline-alkaline clays were explored. 【Result】 The results showed that rewetting significantly promoted the aggregation of clays, which was further enhanced by PBAT-BNPs but was hindered by the high salinity-alkalinity of clays. During the rewetting treatment period, the cation exchange capacity of PBAT-BNP-added clays increased significantly, whereas their electrical conductivity and pH decreased noticeably. The acidic environment induced by PBAT-BNPs facilitated the dissolution of clay minerals and the release of silicate ions. Under the rewetting condition, the Al cations promoted the formation of aggregates through flocculation. Meanwhile, the release of PBAT monomers and soluble ions from clays led to a significant increase in the interlayer spacing of minerals. 【Conclusion】 This study provides a new perspective on the abiotic impacts of biodegradable nanoplastics on soil properties.