Abstract: The magnesium oxysulfate whiskers (MgOS_W) were modified by silane coupling agent 3-triethoxysilylpropylamine(KH550), and the modified whiskers dispersion liquid was prepared by ultrasonic technology. MgOS_W/natural rubber (NR) composites were developed by the blending modified whiskers dispersion liquid with the NR latex. The morphology, mechanical properties, flammability properties and thermalstability properties of the KH550-MgOS_W/NR composites were investigated. The results show that modified MgOS_W have good compatibility with NR latex matrix. The properties of KH550-MgOS_W/NR composites are improved by the incorporation of modified MgOS_W into NR matrix.When modified whiskers mass ratio to NR is 4%, the performances of KH550-MgOS_W/NR composites achieve optimum results. Compared with pure NR, the modulus at 300%, tensile strength, tear strength, elongation at break and crosslink density of KH550-MgOS_W/NR composites are increased by 25.0%, 36.8%, 37.3%, 11.4%, 44.2%, respectively. The flame retardant grade of composites increases from FV-1 to FV-0. The initial thermal degradation temperature (T₀), maximum thermal degradation temperature (T_p), and termination of thermal degradation temperature (TT_f) of KH550-MgOS_W/NR composites markedly increase 6.2℃, 5.2℃ and 4.1℃, respectively, compared to NR.