Based on the first-principles calculations, we systematically study the electronic structures and topological properties of bismuth (Bi) ultrathin films in (111) orientation. Considering the spin–orbit coupling, the Bi(111) films show the thickness dependent behavior of their band structures and topological properties. The single and two bilayers Bi(111) films are confirmed to be nontrivial two-dimensional (2D) topological insulator system, while for the films from three to five bilayers, a transition from semiconductor to semimetal is found. Moreover, the single bilayer Bi(111) thin film is very robust against external electric field, but the two bilayers film is not robust.