A kind of superhydrophobic/superoleophilic kapok fiber for separating oil/water mixtures and oil-in-water emulsions was successfully fabricated. The facile preparation procedure includes uniform growth of ZnO nanoneedles on the surface of kapok fiber via one-step hydrothermal method and subsequent hydrophobic modification with dodecanethiol (DDT). The as-prepared fiber shows high sorption capacities up to 40.8–70 times its self-weight for a series of oils and organic solvents, quick oil sorption rate, and selective sorption to oils in water. Furthermore, superhydrophobic fiber assembly connected to a vacuum system is able to continuously remove and collect a large amount of oils within a short time. More importantly, the obtained fiber is capable of separating oil-in-water emulsions with high separation efficiency (transparency: >86.4%). The coated fiber can still keep stable hydrophobicity under harsh conditions (acidic, alkaline, salty solutions, oils, and hot water). The as-prepared sorbent is low cost and environmental friendly, which makes it a promising candidate to be used in effective oil-spill cleanups and water purification.