High-quality single crystalline niobium films are grown on a-plane sapphire in molecular beam epitaxy.The film is single crystalline with a (110) orientation,and both the rocking curve and the reflection high-energy electron diffraction patte demonstrate its high-quality with an atomically smooth surface.By in situ study of its electronic structure,a rather weak electron-electron correlation effect is demonstrated experimentally in this 4d transition metal.Moreover,a kink structure is observed in the electronic structure,which may result from electron-phonon interaction and it might contribute to the superconductivity.Our results help to understand the properties of niobium deeply.