A superhydrophilic/underwater superoleophobic magnetic cellulose and acrylamide-modified polyurethane foam (Fe₃O₄-CE-AM@PUF) was prepared for effective gravity-driven oil/water separation. The prepared materials were characterized for their structure and morphology using various characterization techniques. The prepared carbohydrate polymeric composite showed excellent superhydrophilic/underwater superoleophobic properties with a good static underwater oil contact angle of 160°. Furthermore, it exhibited remarkable oil-repellent properties in acidic, basic, and saline water. Fe₃O₄-CE-AM@PUF could also be used after immersion in water for 100 h, and also delivered an excellent underwater superoleophobic performance with an underwater oil contact angle of 155°. Moreover, it demonstrated a high separation efficiency (>99.15%) and an excellent flux up to 31181 $\mathrm{L}{\mathrm{m}}^{-2}{\mathrm{h}}^{-1}$ for various kinds of oil-water mixtures. The separation flux and efficiency of n-Hexane have not significantly changed after 50 cycles of separation. Fe₃O₄-CE-AM@PUF's high porosity, superhydrophilic, and superoleophobic properties allowed it to continuously absorb water from oils. Its magnetic properties made it easy to remove the absorbent material with a magnet.