The treatment of oily wastewater is a global challenge owing to its diverse repercussions on environment and human life. The nanoporous complex membrane consisted of cellulose nanocrystals (CNC), chitin nanocrystals (ChiNC) and chitosan (CH) is fabricated on top of the poly (ethylene terephthalate) (PET) nonwoven fabric via a vacuum-assisted filtration method. The interactions among CNC, ChiNC and CH cause the formation of the membrane which shows underoil superhydrophobic property. The CH is demonstrated to play a key role in contributing to the hydrophobicity of membrane. Without any further treatment, the CNC/ChiNC/CH membrane is capable to separate water from water-in-oil emulsion with a high rejection. The separation performance is affected by the thickness of the prepared membrane which directly relates to the concentrations of the complex solutions. Such polysaccharide-based complex membranes with facile fabrication and low cost are promising for use in the field of oil/water separation.