The present study describes a low-temperature metal-metal bonding process using leaf-like CuO aggregates. A CuO nanoparticle colloid solution was prepared at 20 degrees C with a salt-base reaction. Leaf-like CuO aggregates with a longitudinal size of ca. 990 nm and a lateral size of ca. 440 nm composed of CuO nanoparticles with a size of ca. 10 nm were fabricated by aging the CuO particle colloid solution at 80 degrees C. The metal-metal bonding ability of the leaf-like CuO aggregates was examined by pressurizing metallic discs sandwiching the CuO particles as a filler at 1.2 MPa for 5 min under annealing in H-2 gas. The metal-metal bonding could be performed even for an annealing temperature as low as 250 degrees C. A shear strength of 17.0 MPa was recorded for the annealing temperature of 250 degrees C.