A novel and facile method that needs only a few steps of dissolution, gelation and supercritical carbon dioxide (ScCO₂) drying has been developed to fabricate ultralow density cellulose triacetate aerogels (TAC). In this method, using dioxane as a solvent and isopropanol as a non-solvent, regeneration and solvent exchange are not necessary due to the phase separation and heat-induced gelation and the good solubility of dioxane/isopropanol in ScCO₂, thus leading to a more efficient synthesis and better quality of aerogels in terms of less shrinkage and breakage. The relationship between the theoretical density and the actual density of the TAC aerogel is discussed, and the actual density of the aerogels could be well tuned in the range between 5 mg cm⁻³ and 50 mg cm⁻³. These newly developed nanostructured TAC aerogels were characterized using scanning electron microscopy (SEM) and nitrogen adsorption. All the prepared aerogels showed both a nanostructured solid network and a nanoporous network, together with specific fiber sizes of about 30 nm. The fiber thickness and pore sizes are much lower than that of the normal porous polymer materials. The specific surface area of the aerogels with different density ranged from 229 m² g⁻¹ to 958 m² g⁻¹, as measured by nitrogen adsorption tests. The porosity of all these aerogels was higher than 96%. The thermodecomposition behavior of TAC aerogels and the original TAC granules was almost the same, with a rather high decomposition temperature.