A solventless laminating adhesive comprising a polyisocyanate component and a polyol component, both of which are free from polyol components exhibiting crystalline properties at ordinary temperatures. The adhesive exhibits an initial viscosity of 500 to 1000 mPa s three minutes after mixing of the polyisocyanate component with the polyol component and a viscosity increase of 100 to 350% based on the initial viscosity 20 minutes after the mixing. In a coater which is provided with a pair of opposed rolls and in which the rolls rotates in the directions contrary to each other at the opposition site, the adhesive is applied to a film passing between the rolls.