The lowest-energy structures of the Al(n)Be (n = 1-13) clusters are obtained and compared with the corresponding Al(n+1) and Al(n+1)(+) (n = 2-13) as well as Al(n)Mg clusters at the B3LYP/aug-cc-pVDZ level. The configurations of Al(n)Be show strong resemblances to those of pure Al(n+1) clusters, and the first three-dimensional ground state in the Al(n)Be clusters occurs for Al(3)Be. Various properties of the Al(n)Be clusters are systematically investigated using the CCSD(T) method and their thermodynamic properties are also compared with those of corresponding Al(n+1)(+) clusters. The evolution of the energetic and electronic properties with the size of the clusters shows the unique stability of the 20-valence electron systems Al(6)Be and Al(7)(+), which can be understood from the spherical jellium model (SJM). However, different from Al(7)(+) with 1s(2)1p(6)1d(10)2s(2) shell occupation, the electronic-shell structure of 1s(2)1p(6)1d(6)2s(2)1d(4) for the Al(6)Be cluster demonstrates that the impurity atom makes the molecular orbital distribution of doped clusters much more complex than that of pure metal clusters.