The stable structures, energies, and electronic properties of neutral, cationic, and anionic clusters of Al-n (n = 2-10) are studied systematically at the B3LYP/6-311G(2d) level. We find that our optimized structures of Al-5(+) Al-9(+), Al-9(-), Al-10, Al-10(+), and Al-10(-) clusters are more stable than the corresponding ones proposed in previous literature reports. For the studied neutral aluminum clusters, our results show that the stability has an odd/even alternation phenomenon. We also find that the Al-3, Al-7, Al-7(+), and Al-7(-) structures are more stable than their neighbors according to their binding energies. For Al7 with a special stability, the nucleus-independent chemical shifts and resonance energies are calculated to evaluate its aromaticity. In addition, we present results on hardness, ionization potential, and electron detachment energy. On the basis of the stable structures of the neutral Al-n (n = 2-10) clusters, the AlnO (n = 2-10) clusters are further investigated at the B3LYP/6-311G(2d), and the lowest-energy structures are searched. The structures show that oxygen tends to either be absorbed at the surface of the aluminum clusters or be inserted between Al atoms to form an Aln-1OAl motif, of which the Aln-1 part retains the stable structure of pure aluminum clusters.