A thermally stable and hydrophobic cellulose nanofibril (CNF)-silica composite aerogel was prepared by simply immersing the CNF aerogel into the silica sol with different tetraethyl orthosilicate (TEOS) concentration and shaping it by means of low-risk ambient pressure drying. After the introduction of the mesoporous silica particles into the cellulose network structure, the BET surface area was found to have sharply increased from 11.3 to 497.8 m(2) g(-1). All composite aerogels displayed good thermal stability and super-hydrophobicity compared with pure cellulose aerogel. The onset temperature of pyrolysis rose from 317 to 348 A degrees C, and the contact angle reached 152.1A degrees. The TEOS concentration was found to have a great influence on the silica content and the dispersion of silica particles in the cellulose scaffold. Good chemical compatibility at the nanoscale level was present, which indicates that a continuous and homogeneous CNF-silica interface would yield great improvement in thermal properties and water resistance. The results show that a composite aerogel prepared at 2.5 mol L-1 TEOS concentration has better comprehensive performance with only a slightly decrease in mechanical properties compared to CNF aerogel. Thus, this study details a new direction for the synthesis of a cellulose-silica composite aerogel with tailored properties achieved by controlling the silica content and silica dispersion in the cellulose scaffold. Thermally stable, water-resistant, and environmentally friendly cellulose-silica composite aerogels may provide a promising development for designing new functional aerogels that can be applied in various fields.