An optimization strategy combining global semi-empirical quantum chemistry search with all-electron density functional theory was adopted to determine the lowest energy structure of B19Al clusters. B19Al is a nearly perfect planar, which is remarkably different from that of tubular neutral B-20 cluster. The Al atom occupies a peripheral position of the planar, which results from the difference in atomic size and cohesive energy between aluminum and boron atoms. Meanwhile, the planarity of B19Al cluster is attributed to s-p(2) hybridization. Some properties, including chemical bonding, HOMO-LUMO gaps, molecular orbital distribution, electric dipole moments, and charge transfer and distribution, are discussed. The doped planar boron clusters can be created by doping with Al atom.