the objective of this research was to evaluate the effect of the acid hydrolysis of eucalyptus grandis w. hill ex maiden bark tannins on the properties of tannic adhesives. adhesives were synthesized with tannins hydrolyzed at four ph values, three reaction times and 10% of formaldehyde based on the tannin dry weight. ninety-six glued joints were prepared with eucalyptus grandis thin boards. shear resistance and wood failure percentage were determined according to the astm d 2339-93 standards. it was concluded that tannin hydrolysis decreased adhesive viscosity and increased the glue line shear resistance. however, it was observed a low percentage of wood failure.