In this work, ceramics 3D printing combined with in situ grown whiskers are proposed for effective oil/water separation in multiple conditions, including (i) free oil/water mixture, (ii) oil purification, and (iii) separation of an oil-in-water emulsion. 3D printing allows the realization of geometrically complex alumina structures, inclusive of honeycomb meshes, sponges, woodpile scaffolds with flexible configuration of inner channels and struts. Aluminum borate whiskers, featured with superhydrophilicity and underwater superoleophobicity, are synthesized on those printed alumina substrates, acting as the pivotally functional coating. These combined structures possess excellent oil/water separation efficiency (over 99%) and high flowrate. The all-ceramic structures also exhibit remarkable durability in cycling tests and resistance to harsh environment, such as organic solvent, elevated temperature and highly corrosive solution, compared with metal/polymer counterparts. Finally, these all-ceramic filters can be quickly restored by high-temperature heat treatment to remove attached oil or water, so that the filters can be reused to avoid waste generation.