Average gas holdup, phi, and liquid mixing time, t(M), were experimentally investigated in a bubble column (0.32 m i.d.) equipped with perforated plates having four types of hole arrangements. Each plate had 88 holes of 0.5 mm in diameter, which were arranged as follows; Type A: regular triangle (pitch = 30 mm) Type B: regular triangle (pitch = 7 mm) Type C: equal intervals on concentric circles of 0.256 m and 0.288 m in diameter Type D: regular triangle (pitch = 10 mm) leaning against the column wall The unaerated liquid height was 0.64 m in all runs. For the four types of perforated plates, the measured values of phi increased with increasing superficial gas velocity, u(G0). The hole arrangement strongly influenced phi. For the entire range of u(G0) covered in this study, the highest values of phi were obtained with the perforated plate of Type C, and the smallest values were obtained with Type D. However, the hole arrangement had no effect on the values of t(M), which were almost constant under the experimental conditions employed.