Photodetachment photoelectron spectroscopy experiments on NbnAl-clusters have been carried out in a size range n = 4 to 12 at 3.49 eV photon energy. The evolution of the electronic structure is discussed as a function of cluster size and composition. Electron affinities (EA) and vertical detachment energies are determined. One central point of this study is the direct comparison of the electronic structure of pure and Al-doped Nb-n(-) clusters in the threshold binding energy region with regard to hybridization effects. Direct correlation between electronic structure and H-2 chemisorption. rate constants reported by Nonose et al. [Chem. Phys. Lett. 164 (1989) 427], is found for n = 5 to 8 and n > 9.