The alcogel prepared by sol-gel process of polydiethoxysiloxane (PDEOS) according to the mass ratio of C₂H₅OH∶ PDEOS∶HF∶H₂O=20∶10∶3∶0.5, was modified by methyltriethoxysilane(MTES) and washed with alcohol and n-hexane. The obtained gel was then dried under ambient pressure to prepare hydrophobic SiO₂ aerogel. It is shown that hydrophobic SiO₂ aerogels can be obtained when the mass ratio of MTES/ PDEOS is higher than 1.2. The contact angle between hydrophobic SiO₂ aerogels and water is larger than 110°, the densities and specific surface areas of hydrophobic SiO₂ aerogels are in the range of 125～160kg/m³ and 560～900m²/g respectively.