Abstract: Sodium montmorillonite (MMT) was modified by octadecyl trimethyl ammonium chloride (OTAC) via cation exchange to obtain organo-montmorillonite (OMMT), Al₂O₃ was modified by silane coupling agent KH550 to get KH-Al₂O₃. The polyurethane elastomer (PUE) was synthesized with 4,4'-diphenylmethane diisocyanate (MDI), polypropylene glycol (PPG) and 1,4-butanediol (BDO) as the raw materials, different mass ratio of OMMT to KH-Al₂O₃ with a fixed 3wt% content as the modifier, the OMMT-modified Al₂O₃/PUE(OMMT-Al₂O₃/PUE) composites were prepared by prepolymer method. The micro-morphology and mechanical properties of OMMT-Al₂O₃/PUE composites were measured. The results of FTIR, XRD and TEM show that the characteristic peaks of -CH₂ (2 922 cm^-1 and 1 469 cm^-1) appear, indicating that new groups are introduced into the layers of MMT, and the interlayer spacing of OMMT is about 0.7 nm bigger than that of MMT. The characteristic peaks of -CH₂ (2 924 cm^-1 and 1 447 cm^-1) appear, proving that KH550 is successfully grafted to the surface of Al₂O₃. The layer structure of OMMT can be clearly seen, and OMMT and KH-Al₂O₃ have good dispersion in the PUE matrix. SEM and XRD reveal that proper OMMT and KH-Al₂O₃ disperse evenly in the PUE matrix, and OMMT exists in the form of single layer in the OMMT-Al₂O₃/PUE composites. There is a certain interaction between OMMT and KH-Al₂O₃, and the interactions within the same molecule are reduced. The test results of mechanical properties of OMMT-Al₂O₃/PUE composites display that the maximum tensile strength, elongation at break and breaking tensile strength of OMMT-Al₂O₃/PUE composites are 21.82 MPa, 668% and 19.98 MPa, 43.8%, 29.2% and 36.8% higher than that of PUE matrix, respectively, when the mass ratio of OMMT to Al₂O₃ is 1:1. The mechanical properties of OMMT-Al₂O₃/PUE composites are significantly better than those of OMMT/PUE or Al₂O₃/PUE composite.