Superior selective adsorption of organic dye is still a big challenge in the process of dye wastewater treatment. Meanwhile, low-price and environmentally friendly biomass-based adsorbents show huge potential in the fields of separation and purification. In this study, we adopted the "hydrolysis-calcination method" to develop a novel in situ anchoring strategy for ultrasmall TiO(2-x) on carbonized bacterial cellulose (CBC), which was derived from natural bacterial cellulose. Notably, 3D networks of porous CBC played a dual role for both providing hydrolytic sites and controlling the oxygen vacancies (V(o)) of TiO(2-x). As for the single-dye adsorption, the TiO(2-x)/CBC had a strong adsorption ability (101.4 mg/g) for removing methylene blue (MB), which was much higher than that of methyl orange (MO), malachite green (MG), rhodamine B (RhB), and tetracyclines (TC). Moreover, under the optimized carbonization temperature (T(c)) of 300 °C, the TiO(2-x)/CBC-300 exhibited an outstanding separation efficiency of 97.07% for the MB/MO solution. Detailed analysis confirmed that T(c) was a key regulator for adjusting the V(o) concentration, which directly influenced the surface charge density and, further, the separation efficiency of TiO(2-x)/CBC. Additionally, the used adsorbent could be easily regenerated from washing by ethanol. After 4 regenerations, the adsorption efficiency declined only by 6.9% after 20 min and 13.6% after 120 min adsorption, respectively. Ultimately, this oxygen vacancy-rich TiO(2-x)/BC system illuminated good prospects for mixed dye wastewater adsorption and separation.