Abstract: The purpose of this study is to assess the impact of microplastic residual from polyurethane (PU) coated controlled-release fertilizer on the rates of soil organic carbon mineralization and straw degradation. Soil samples collected from the coastal area of Jiangsu Province were tested for differences in the soil organic carbon mineralization rate, total content of organic carbon and enzymatic activity when microplastics, straw, or both, were added to soil. The soil conditions tested were: control with no added materials (CK), 0.1% (mass fraction) microplastics (T1), 0.3% microplastics (T2), 1% microplastics (T3), 1% straw (S), and all subsequent combinations of microplastics with straw. Over the course of 35 days, 1% microplastics or microplastics plus straw (T3, T1+S, T2+S and T3+S) significantly promoted soil organic carbon mineralization, while lower amounts of microplastics (T1 and T2) had no significant effect. T1, T2 and T3 significantly increased the cumulative soil mineralization amount by 72.77%-80.00%. Furthermore, microplastics and straw also increased the amounts of soil soluble organic carbon (DOC), microbiological biomass carbon (MBC) and easily oxidized organic carbon (ROC). Compared with the control (CK) treatments T1, T2, and T3 significantly increased the DOC, MBC and ROC by 5.70%-57.43%、9.14%-41.92% and 2.87%-57.34%, respectively. Compared with straw treament (S) alone, the presence of both microplastics and straw having an additive effect on abundance with the increasing of DOC, MBC and ROC by 13.74%-75.82%、10.38%-60.19% and 2.21%-34.76%, respectively. Furthermore, both microplastics and straw supplementation significantly increased the activities of β-glucosidase (GLU) and catalase (CAT) in soil, exemplifying a generally increasing trend in soil organic mineralization and enzymatic activity in the presence of microplastics and straw.