A water-based composition for barrier containing a urethane resin (A) which is comprising a polyol (a1), a polyisocyanate (a2) and a chain extender (a3) as essential reaction components, and at least one wax (B) selected from the group consisting of a paraffin, a carnauba and an alkyl ketene dimer, and further a content ratio between the component (A) and the component (B) in terms of the non-volatile content weight is (A)/(B)=25/75 to 95/5.