Uniform CuO coating of Al18B4O33 whiskers (Al18B4O33w) was prepared by hydrothermal synthesis. CuO reacts with molten 6061Al and MgAl2O4 forms at the interface. CuO coating of whiskers effectively improves tensile properties and hinder the interfacial reactions. CuO coating content has a great effect on the tensile properties of the composite. After CuO coating of whiskers, the peak-aged time of the composite prolongs.