In this paper, by using a linear combination of atomic orbitals approach with the density func-tional formalism, the stuctures and the magnetic properties of FenB clusters (n=1-6) have been studied in detail. It is found that the B atom is favored to locate at the surface not the center of the cluster, and the tetrahedron for Fe4B and the triangular prism for Fe6B clusters are not the most stable structures. When one atom in Fen+1 cluster is replaced by a B atom forming FenB cluster, the binding energy increases, while the moment of Fe atom decreases. The variation of average moment with the atomic percentage of B atom is nonlinear in FenB cluster, differing from the behavior of bulk amorphous Fe-B alloys. It is indicated that the environmemt and doping play an important role on the stability and magnetic properties of cluster.