Microscopic features of liquid and amorphous alumina $(Al_{2}O_{3})$ were simulated by molecular dynamics calculations. The simulations were performed in an orthorhombic cell with 3000 particles using the Born-Mayer potential at temperatures of 0, 2500, 2700, and 3000 K under constant pressure. It was found that a large cluster of pores contained several thousand spherical pores, which were formed with radii larger than $0.73;{AA}$. The observed variations of $Al_{2}O_{3}$ structures with atomic arrangements of $AlO_x$ (x = 3, 4, 5, and 6) are discussed.