In recent years, the Taiwan government has implemented numerous financial reforms. The main aims of these reforms has been to lower excessive competition among financial institutions by raising their concentration and to improve the efficiency of financial institutions. This paper presents an empirical study on the impact of bank concentration and bank efficiency on bank competition in Taiwan from 1996 to 2007. This paper finds that the relation between bank concentration and bank competition is nonlinear. While bank concentration is low, increasing bank concentration results in increasing bank competition. While bank concentration is high, increasing bank concentration results in decreasing bank competition. This paper also finds that higher bank efficiency lowers bank competition.