Poly(N-vinylformamide) microgel, crosslinked by 1,3-divinylimidazolid-2-one (BVU), was synthesized via precipitation polymerization in methyl ethyl ketone (MEK), giving aggregated particles with a broad size distribution. Alkaline hydrolysis yielded a series of poly(vinylamine) (PVAm) microgels. The wet adhesion properties of the microgels on a regenerated cellulose membrane were studied by delamination experiments, and the results were compared with that of a linear PVAm. Above the polymer coverage (i.e., the amount of polymer in the adhesive joint) of 15 mg/m(2), the linear polymer and the microgel give similar adhesion, and higher polymer coverage does not increase the wet strength any further. However, when the polymers are applied on the wet cellulose membranes by adsorption from solution, the delamination force of the membranes with the microgel was much stronger than those with the linear polymer, because the microgel formed a much thicker polymer layer on membranes. Confocal laser scanning microscopy (CLSM) images of laminates prepared with fluorescently labeled polymers and microgels revealed that the linear polymer gives cohesive failure during peeling test, while adhesive failure is dominant for the microgel.