Al2O3 nanowires and Si nanowires with wrapping layers of amorphous Al2O3 have been synthesized by heating a mixture of Al, SiO2 and Fe2O3 catalyst supported on alumina at different temperatures. The results indicate the growth of the two nanowires competes against each other and depends on the reaction temperature. The addition of SiO2 is not essential for synthesizing Al2O3 nanowires. Al2O3 nanowires can be synthesized by directly heating Al with some catalysts when oxygen was introduced. In situ catalytic growth and silica-assisted effect are also discussed.