It is a challenge to fabricate three-dimensional carbon aerogels based on natural renewable resources with stability, flexibility, and versatility. Here, an ultralight, elastic, and hydrophobic multifunctional reduced graphene oxide-konjac glucomannan (RGO-KGM) carbon aerogel was fabricated by a three-step process of freeze-casting, freeze-drying, and carbonization. In the freeze-casting process, three unique structural RGO-KGM carbon aerogels were obtained by adjusting the position of the PDMS mold on the homemade directional freezer. RGO-KGM carbon aerogels possessed many excellent physicochemical properties, such as ultralow density, high specific surface area, elasticity, hydrophobicity, and controllable size. As an adsorbent, RGO-KGM carbon aerogels exhibited high adsorption capacity for various organic solvents and oils, and the maximum adsorption capacity reached up to 360 g/g. Therefore, RGO-KGM carbon aerogels with good mechanical properties and reusability shows promising prospects in the field of water treatment.