Abstract: The adhesive forces of Nb-Nb(110), Nb-Ta(110), Nb-W(110) and Nb-Ti have been measured in ultra-high-vacuum(10-7Pa). The real contact areas were calculated by a multiasperities contact dynamic model. The experimental results of their adhesive strength range from 0.2 to 2.0 eV/atom, which are in agreement with theoretical values calculated by a simple tight-binding self-consistent moment method. These facts indicate that across the interface there is an interaction, which arises from chemical bonding is caused by sharing of electrons between two transition metals and mainly controlled by the density of states of their d-electrons. The adhesive strength decreases greatly because of the segregations of C, N, B and S etc. nonmetallic impurities with elevating the temperature of the samples.