Abstract: The preparation of PLA/coffee ground composites modified with diphenylmethane diisocyanate (MDI) was carried out by a melt-mixing method, and the resulting composites were formed by using supercritical CO2 as a foaming agent. The thermal, rheological and mechanical properties of composites were studied and their foaming behavior was investigated. The rheological results indicated that the melt elasticity of composites was improved in the presence of MDI due to a chain-extending reaction. The thermal and mechanical properties of composites were also influenced by MDI and coffee grounds. A bimodal behavior was observed in differential scanning calorimetric thermograms due to the melting and cold crystallization of PLA. The degree of cold crystallinity of PLA was improved up to 24.68 % due to the chain extension of MDI, which also resulted in an improvement in the impact resistance of the composites. Moreover, the composite foams achieved a cell density of 9.26×106 cell/cm3 and a foaming expansion ratio of 9.33. This indicated that the incorporation of MDI favored an improvement in melt elasticity for PLA/coffee ground composite and thus could well control the cellular structure of PLA foams.